| 566. Reshape the Matrix |
Easy |
变长数组，求余法，维护行列计算在新的数组中的位置 |
https://blog.csdn.net/fuxuemingzhu/article/details/83626519 |
| 897. Increasing Order Search Tree |
Easy |
直接中序遍历的结果放到链表结尾 |
https://blog.csdn.net/fuxuemingzhu/article/details/82349263 |
| 771. Jewels and Stones |
Easy |
字典统计次数 |
https://blog.csdn.net/fuxuemingzhu/article/details/79188903 |
| 929. Unique Email Addresses |
Easy |
字符串+set统计个数 |
https://blog.csdn.net/fuxuemingzhu/article/details/83478570 |
| 709. To Lower Case |
Easy |
ASIIC码操作ord,chr |
https://blog.csdn.net/fuxuemingzhu/article/details/81015228 |
| 804. Unique Morse Code Words |
Easy |
字典映射 + set统计个数 |
https://blog.csdn.net/fuxuemingzhu/article/details/79774003 |
| 905. Sort Array By Parity |
Easy |
自定义sorted函数的cmp为数字mod 2 |
https://blog.csdn.net/fuxuemingzhu/article/details/82732066 |
| 461. Hamming Distance |
Easy |
先异或 再数1的个数 |
https://blog.csdn.net/fuxuemingzhu/article/details/54138423 |
| 657. Robot Return to Origin |
Easy |
Counter统计，判断是否相等 |
https://blog.csdn.net/fuxuemingzhu/article/details/83663650 |
| 832. Flipping an Image |
Easy |
直接计算新的数组的每个位置的值即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/80471495 |
| 617. Merge Two Binary Trees |
Easy |
树的递归操作 |
https://blog.csdn.net/fuxuemingzhu/article/details/79052953 |
| 28. Implement strStr() |
Easy |
字符串遍历+切片是否相等的判断 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254558 |
| 890. Find and Replace Pattern |
Easy |
直接使用字典做映射 |
https://blog.csdn.net/fuxuemingzhu/article/details/82014687 |
| 814. Binary Tree Pruning |
Medium |
二叉树的后序遍历 |
https://blog.csdn.net/fuxuemingzhu/article/details/79858752 |
| 561. Array Partition I |
Easy |
排序+求和 |
https://blog.csdn.net/fuxuemingzhu/article/details/71412574 |
| 728. Self Dividing Numbers |
Easy |
直接遍历区间的每个数字进行判断 |
https://blog.csdn.net/fuxuemingzhu/article/details/79053113 |
| 852. Peak Index in a Mountain Array |
Easy |
二分查找的变种，使用Mid位置和左右位置比较 |
https://blog.csdn.net/fuxuemingzhu/article/details/80721162 |
| 922. Sort Array By Parity II |
Easy |
分别求出奇偶数组然后拼接 |
https://blog.csdn.net/fuxuemingzhu/article/details/83045735 |
| 883. Projection Area of 3D Shapes |
Easy |
分别计算三视图的面积即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/81748335 |
| 908. Smallest Range I |
Easy |
直接数学计算 |
https://blog.csdn.net/fuxuemingzhu/article/details/82824685 |
| 867. Transpose Matrix |
Easy |
先构建数组再遍历实现翻转 |
https://blog.csdn.net/fuxuemingzhu/article/details/81015450 |
| 589. N-ary Tree Preorder Traversal |
Easy |
多叉树的先序遍历，可以用递归和迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/81021950 |
| 590. N-ary Tree Postorder Traversal |
Easy |
多叉树的后序遍历 |
https://blog.csdn.net/fuxuemingzhu/article/details/81017965 |
| 350. Intersection of Two Arrays II |
Easy |
先排序然后用两个指针移动找出数组交集 |
https://blog.csdn.net/fuxuemingzhu/article/details/54341965 |
| 876. Middle of the Linked List |
Easy |
快慢指针同时向链表后面移动 |
https://blog.csdn.net/fuxuemingzhu/article/details/81748484 |
| 700. Search in a Binary Search Tree |
Easy |
BST中节点的查找，递归 |
https://blog.csdn.net/fuxuemingzhu/article/details/81015754 |
| 933. Number of Recent Calls |
Easy |
找出满足一定条件的区间长度，可以使用二分或者队列 |
https://blog.csdn.net/fuxuemingzhu/article/details/83714891 |
| 559. Maximum Depth of N-ary Tree |
Easy |
求树的高度，可以使用BFS和DFS |
https://blog.csdn.net/fuxuemingzhu/article/details/81021864 |
| 557. Reverse Words in a String III |
Easy |
字符串的单词分别翻转再拼接到一起就好了 |
https://blog.csdn.net/fuxuemingzhu/article/details/70141268 |
| 806. Number of Lines To Write String |
Easy |
使用字典保存每个字符的长度，然后统计每行的长度是否超过100就好了 |
https://blog.csdn.net/fuxuemingzhu/article/details/79810381 |
| 344. Reverse String |
Easy |
字符串翻转，[::-1 |
https://blog.csdn.net/fuxuemingzhu/article/details/51284382 |
| 811. Subdomain Visit Count |
Easy |
字典保存每个子域名出现的次数即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79789925 |
| 476. Number Complement |
Easy |
求数字的补数，方法是异或上与其二进制数字的长度相等的全1二进制数 |
https://blog.csdn.net/fuxuemingzhu/article/details/54562124 |
| 821. Shortest Distance to a Character |
Easy |
过两遍数组，分别找出距离左边和右边的这个字符的最短距离 |
https://blog.csdn.net/fuxuemingzhu/article/details/80471765 |
| 500. Keyboard Row |
Easy |
使用字典保存每行元素，然后看每个单词是不是只由一行元素组成 |
https://blog.csdn.net/fuxuemingzhu/article/details/68953517 |
| 893. Groups of Special-Equivalent Strings |
Easy |
把奇偶位置都取出来，重新拼接成字符串作为指纹，看总的有多少种指纹 |
https://blog.csdn.net/fuxuemingzhu/article/details/82083609 |
| 872. Leaf-Similar Trees |
Easy |
先序、中序、后序都能得到叶子序列 |
https://blog.csdn.net/fuxuemingzhu/article/details/81748617 |
| 884. Uncommon Words from Two Sentences |
Easy |
使用字典统计每个单词出现的次数，然后看字典keys()的交集，然后在字典中看是不是只出现了一次 |
https://blog.csdn.net/fuxuemingzhu/article/details/81749170 |
| 766. Toeplitz Matrix |
Easy |
判断每个斜线是否相等，方法是判断每个元素是否和其左上角元素相等 |
https://blog.csdn.net/fuxuemingzhu/article/details/79127213 |
| 463. Island Perimeter |
Easy |
求小岛的周长。使用所有陆地个数×4-相交部分×2. |
https://blog.csdn.net/fuxuemingzhu/article/details/83868905 |
| 682. Baseball Game |
Easy |
用一个栈进行模拟 |
https://blog.csdn.net/fuxuemingzhu/article/details/79183412 |
| 868. Binary Gap |
Easy |
二进制表示中1的最大间距，保留上一个1的位置即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/81079495 |
| 104. Maximum Depth of Binary Tree |
Easy |
二叉树的高度，可以用DFS和BFS |
https://blog.csdn.net/fuxuemingzhu/article/details/48490829 |
| 136. Single Number |
Easy |
所有的数字出现了两次，其中一个只出现了一次。找出这个数字的方法可以使用字典统计或者异或运算 |
https://blog.csdn.net/fuxuemingzhu/article/details/54173334 |
| 496. Next Greater Element I |
Easy |
找出某个数字右边比他大的数字，直接遍历查找就好了 |
https://blog.csdn.net/fuxuemingzhu/article/details/79080337 |
| 637. Average of Levels in Binary Tree |
Easy |
求每层的二叉树的均值，可以使用BFS和DFS |
https://blog.csdn.net/fuxuemingzhu/article/details/79088554 |
| 693. Binary Number with Alternating Bits |
Easy |
判断数字的二进制表示是不是01交错的。直接遍历判断，或者位运算。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79089937 |
| 762. Prime Number of Set Bits in Binary Representation |
Easy |
判断二进制数字的1的个数是不是质数 |
https://blog.csdn.net/fuxuemingzhu/article/details/79089092 |
| 917. Reverse Only Letters |
Easy |
只翻转字母其余字符不动，可以使用栈、双指针 |
https://blog.csdn.net/fuxuemingzhu/article/details/82956271 |
| 292. Nim Game |
Easy |
判断输入数字是不是4的倍数即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/51284421 |
| 824. Goat Latin |
Easy |
字符串处理，简单 |
https://blog.csdn.net/fuxuemingzhu/article/details/80471925 |
| 892. Surface Area of 3D Shapes |
Easy |
统计立方体个数，减去相交面积 |
https://blog.csdn.net/fuxuemingzhu/article/details/82083893 |
| 784. Letter Case Permutation |
Easy |
经典回溯法，把字符的大小写分别拼接到字符串尾部 |
https://blog.csdn.net/fuxuemingzhu/article/details/79360330 |
| 258. Add Digits |
Easy |
两重循环，一直对每位数字求和直到剩余个位数 |
https://blog.csdn.net/fuxuemingzhu/article/details/49161129 |
| 283. Move Zeroes |
Easy |
使用一个指针指向第一个为0的位置，然后遍历不是0的位置进行交换 |
https://blog.csdn.net/fuxuemingzhu/article/details/51284981 |
| 748. Shortest Completing Word |
Easy |
找出符合某个模式的字符串，直接处理就好了 |
https://blog.csdn.net/fuxuemingzhu/article/details/79432228 |
| 690. Employee Importance |
Easy |
dfs |
https://blog.csdn.net/fuxuemingzhu/article/details/79091343 |
| 389. Find the Difference |
Easy |
找多出来的字符，可以使用字典，也可以使用异或 |
https://blog.csdn.net/fuxuemingzhu/article/details/54174443 |
| 520. Detect Capital |
Easy |
统计大写字符的个数，判断是不是在首位 |
https://blog.csdn.net/fuxuemingzhu/article/details/68957658 |
| 448. Find All Numbers Disappeared in an Array |
Easy |
用set去重，找出没有出现的数字即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/53981307 |
| 696. Count Binary Substrings |
Easy |
先找出连续的0，1个数，然后进行交错求最小值，在求和 |
https://blog.csdn.net/fuxuemingzhu/article/details/79183556 |
| 454. 4Sum II |
Easy |
4sum，先确定两个数字，然后看剩余两个数字的和是否出现过 |
https://blog.csdn.net/fuxuemingzhu/article/details/79473739 |
| 788. Rotated Digits |
Easy |
字典保存翻转后的数字，判断是否相等即可。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79378135 |
| 653. Two Sum IV - Input is a BST |
Easy |
BFS或者DFS，在遍历的过程中进行破案吨 |
https://blog.csdn.net/fuxuemingzhu/article/details/79120732 |
| 371. Sum of Two Integers |
Easy |
位运算 |
https://blog.csdn.net/fuxuemingzhu/article/details/79379939 |
| 349. Intersection of Two Arrays |
Easy |
用两个set求交集，然后转成List即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/54236183 |
| 606. Construct String from Binary Tree |
Easy |
先序遍历，可以省略右子树，所以需要做一个节点是否存在的判断 |
https://blog.csdn.net/fuxuemingzhu/article/details/79121550 |
| 206. Reverse Linked List |
Easy |
翻转单链表，可以使用递归和迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290121 |
| 169. Majority Element |
Easy |
Moore投票法，或者字典统计次数 |
https://blog.csdn.net/fuxuemingzhu/article/details/51288749 |
| 171. Excel Sheet Column Number |
Easy |
26进制，没有难度 |
https://blog.csdn.net/fuxuemingzhu/article/details/51286467 |
| 13. Roman to Integer |
Easy |
使用字典保存映射，遍历求值就好了。 |
https://blog.csdn.net/fuxuemingzhu/article/details/48208995 |
| 937. Reorder Log Files |
Easy |
分割排序，再拼接 |
https://blog.csdn.net/fuxuemingzhu/article/details/83961188 |
| 121. Best Time to Buy and Sell Stock |
Easy |
一次遍历，如果后一天比前一天大就买了卖 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291151 |
| 242. Valid Anagram |
Easy |
判断字符串是否是同构的，直接统计词频或者排序 |
https://blog.csdn.net/fuxuemingzhu/article/details/51286195 |
| 860. Lemonade Change |
Easy |
贪心算法，找零钱先找大的面额，如果不够再用小的面额 |
https://blog.csdn.net/fuxuemingzhu/article/details/80913955 |
| 217. Contains Duplicate |
Easy |
判断数组是否有重复，可以统计词频，判断set长度是否相等，排序等方法 |
https://blog.csdn.net/fuxuemingzhu/article/details/51289768 |
| 427. Construct Quad Tree |
Easy |
建立四叉树，使用递归，判断4个叶子全部是0或者1 |
https://blog.csdn.net/fuxuemingzhu/article/details/81836838 |
| 706. Design HashMap |
Easy |
设计一个字典，直接开个很大的数组即可，内存放得下 |
https://blog.csdn.net/fuxuemingzhu/article/details/81017297 |
| 538. Convert BST to Greater Tree |
Easy |
把每个节点变成比它大的节点的值的和，采用逆中序遍历。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79132336 |
| 100. Same Tree |
Easy |
判断两棵数是否相等，直接递归 |
https://blog.csdn.net/fuxuemingzhu/article/details/51285076 |
| 530. Minimum Absolute Difference in BST |
Easy |
中序遍历，保存前一个节点，当前节点的值减去前一个节点的值 |
https://blog.csdn.net/fuxuemingzhu/article/details/69666671 |
| 783. Minimum Distance Between BST Nodes |
Easy |
和上题完全一样 |
https://blog.csdn.net/fuxuemingzhu/article/details/79402127 |
| 383. Ransom Note |
Easy |
使用字典统计每个字符出现的次数，前者小于后者即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/54178342 |
| 796. Rotate String |
Easy |
字符串切片 |
https://blog.csdn.net/fuxuemingzhu/article/details/79521194 |
| 717. 1-bit and 2-bit Characters |
Easy |
单次遍历，判断前面满足的条件下，最后一位是0即可。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79130681 |
| 453. Minimum Moves to Equal Array Elements |
Easy |
把n-1个数字加1，相等于把最大值-1.求和-n*最小值 |
https://blog.csdn.net/fuxuemingzhu/article/details/54177981 |
| 733. Flood Fill |
Easy |
对相同颜色进行染色，可以使用DFS和BFS. |
https://blog.csdn.net/fuxuemingzhu/article/details/79401716 |
| 404. Sum of Left Leaves |
Easy |
求所有左叶子的和，要判断是不是在左边，判断是不是叶子，然后加到结果中 |
https://blog.csdn.net/fuxuemingzhu/article/details/54178595 |
| 447. Number of Boomerangs |
Easy |
统计回旋镖的个数，不能暴力解决，需要使用排列组合公式n*(n-1) |
https://blog.csdn.net/fuxuemingzhu/article/details/54379349 |
| 598. Range Addition II |
Easy |
求队列的最小值即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79398272 |
| 492. Construct the Rectangle |
Easy |
从算术平方根开始找约数即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/68957959 |
| 167. Two Sum II - Input array is sorted |
Easy |
前后指针同时向中间走，找到target之后停止 |
https://blog.csdn.net/fuxuemingzhu/article/details/70232518 |
| 387. First Unique Character in a String |
Easy |
首先做个字符出现次数的统计，然后再次遍历，找出只出现了一次的第一个字符。 |
https://blog.csdn.net/fuxuemingzhu/article/details/84139374 |
| 697. Degree of an Array |
Easy |
求最大的出现次数的所有数字，其最左右出现的位置差的最小值 |
https://blog.csdn.net/fuxuemingzhu/article/details/79146067 |
| 455. Assign Cookies |
Easy |
贪心算法，尽可能给小孩满足其欲望的饼干 |
https://blog.csdn.net/fuxuemingzhu/article/details/54177627 |
| 108. Convert Sorted Array to Binary Search Tree |
Easy |
构建BST，使用中间数进行分割，用递归 |
https://blog.csdn.net/fuxuemingzhu/article/details/70665213 |
| 506. Relative Ranks |
Easy |
相对排名，可以使用堆或者排序或者argsort |
https://blog.csdn.net/fuxuemingzhu/article/details/70173434 |
| 661. Image Smoother |
Easy |
直接暴力求平均即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79156499 |
| 409. Longest Palindrome |
Easy |
统计出现次数的奇偶就可以 |
https://blog.csdn.net/fuxuemingzhu/article/details/54236594 |
| 599. Minimum Index Sum of Two Lists |
Easy |
保存出现的索引和与元素的对应，使用堆保存最小的就行 |
https://blog.csdn.net/fuxuemingzhu/article/details/79138621 |
| 268. Missing Number |
Easy |
理论和-当前和 |
https://blog.csdn.net/fuxuemingzhu/article/details/70332471 |
| 563. Binary Tree Tilt |
Easy |
后序遍历函数返回的是左右子树的差，在里面用变量求和 |
https://blog.csdn.net/fuxuemingzhu/article/details/71440281 |
| 830. Positions of Large Groups |
Easy |
找到长度大于3的连续字符，需要判断结束！！ |
https://blog.csdn.net/fuxuemingzhu/article/details/80472242 |
| 350. Intersection of Two Arrays II |
Easy |
可以排序，也可以使用字典统计次数 |
https://blog.csdn.net/fuxuemingzhu/article/details/54341965 |
| 543. Diameter of Binary Tree |
Easy |
递归求树的深度，同时求左右两个深度的和的最大值 |
https://blog.csdn.net/fuxuemingzhu/article/details/70338312 |
| 551. Student Attendance Record I |
Easy |
统计A的个数，并且判断连续L的个数 |
https://blog.csdn.net/fuxuemingzhu/article/details/70337973 |
| 121. Best Time to Buy and Sell Stock |
Easy |
保存当前的最小值以及最大收益即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291151 |
| 628. Maximum Product of Three Numbers |
Easy |
找出三个数最大的乘积 |
https://blog.csdn.net/fuxuemingzhu/article/details/79169635 |
| 401. Binary Watch |
Easy |
使用combinations函数 |
https://blog.csdn.net/fuxuemingzhu/article/details/54344098 |
| 746. Min Cost Climbing Stairs |
Easy |
动态规划 |
https://blog.csdn.net/fuxuemingzhu/article/details/79188612 |
| 925. Long Pressed Name |
Easy |
使用双指针，统计连续字符出现的次数 |
https://blog.csdn.net/fuxuemingzhu/article/details/83245395 |
| 541. Reverse String II |
Easy |
Python的切片翻转 |
https://blog.csdn.net/fuxuemingzhu/article/details/70141909 |
| 705. Design HashSet |
Easy |
直接开数组就行 |
https://blog.csdn.net/fuxuemingzhu/article/details/81016992 |
| 107. Binary Tree Level Order Traversal II |
Easy |
DFS和BFS都可以 |
https://blog.csdn.net/fuxuemingzhu/article/details/49108449 |
| 504. Base 7 |
Easy |
转成7进制 |
https://blog.csdn.net/fuxuemingzhu/article/details/70194688 |
| 115. Distinct Subsequences |
Easy |
动规，判断当前字符是否相等 |
https://blog.csdn.net/fuxuemingzhu/article/details/84228383 |
| 21. Merge Two Sorted Lists |
Easy |
可以使用递归或者迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291406 |
| 458. Poor Pigs |
Easy |
类似拨号键盘，多维空间求解 |
https://blog.csdn.net/fuxuemingzhu/article/details/81079261 |
| 257. Binary Tree Paths |
Easy |
打印二叉树的路径，使用递归和迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/71249429 |
| 844. Backspace String Compare |
Easy |
字符串可以退格，使用栈轻松解决 |
https://blog.csdn.net/fuxuemingzhu/article/details/80643408 |
| 202. Happy Number |
Easy |
递归和迭代两种做法 |
https://blog.csdn.net/fuxuemingzhu/article/details/49180507 |
| 674. Longest Continuous Increasing Subsequence |
Easy |
简单的动态规划 |
https://blog.csdn.net/fuxuemingzhu/article/details/79220527 |
| 744. Find Smallest Letter Greater Than Target |
Easy |
线性扫描或者二分 |
https://blog.csdn.net/fuxuemingzhu/article/details/79137225 |
| 118. Pascal’s Triangle |
Easy |
提前构造出来，然后处理每行即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/51346488 |
| 671. Second Minimum Node In a Binary Tree |
Easy |
递归的时候找第二小值 |
https://blog.csdn.net/fuxuemingzhu/article/details/79222455 |
| 720. Longest Word in Dictionary |
Easy |
先排序，再找前缀是否存在。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79123277 |
| 27. Remove Element |
Easy |
使用双指针或者标记指针使得前面都是满足要求的，后面都不满足 |
https://blog.csdn.net/fuxuemingzhu/article/details/51303161 |
| 70. Climbing Stairs |
Easy |
动态规划 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290778 |
| 415. Add Strings |
Easy |
直接模拟大整数加法，需要注意进位问题 |
https://blog.csdn.net/fuxuemingzhu/article/details/54380737 |
| 235. Lowest Common Ancestor of a Binary Search Tree |
Easy |
BST找公共祖先，使用递归很简单 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290289 |
| 594. Longest Harmonious Subsequence |
Easy |
统计相邻的数字是否都存在即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79233752 |
| 101. Symmetric Tree |
Easy |
可以使用BFS和DFS两种方法 |
https://blog.csdn.net/fuxuemingzhu/article/details/51345707 |
| 53. Maximum Subarray |
Easy |
动态规划找子数组最大和 |
https://blog.csdn.net/fuxuemingzhu/article/details/71101802 |
| 819. Most Common Word |
Easy |
正则+统计 |
https://blog.csdn.net/fuxuemingzhu/article/details/80472079 |
| 231. Power of Two |
Easy |
判断二进制是不是只有1个1即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290981 |
| 405. Convert a Number to Hexadecimal |
Easy |
转成16进制，难点在于负数的处理：加上1<<32 |
https://blog.csdn.net/fuxuemingzhu/article/details/54426643 |
| 83. Remove Duplicates from Sorted List |
Easy |
递归和循环 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290506 |
| 326. Power of Three |
Easy |
循环和迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290895 |
| 191. Number of 1 Bits |
Easy |
使用位移统计二进制个数 |
https://blog.csdn.net/fuxuemingzhu/article/details/51290376 |
| 437. Path Sum III |
Easy |
找路径的个数，使用DFS*2或者BFS+DFS |
https://blog.csdn.net/fuxuemingzhu/article/details/71097135 |
| 704. Binary Search |
Easy |
二分的模板 |
https://blog.csdn.net/fuxuemingzhu/article/details/81017415 |
| 119. Pascal’s Triangle II |
Easy |
原地翻转可以用倒序遍历 |
https://blog.csdn.net/fuxuemingzhu/article/details/51348629 |
| 232. Implement Queue using Stacks |
Easy |
两个栈实现一个队列 |
https://blog.csdn.net/fuxuemingzhu/article/details/51345762 |
| 572. Subtree of Another Tree |
Easy |
DFS*2或DFS+BSF |
https://blog.csdn.net/fuxuemingzhu/article/details/71440802 |
| 198. House Robber |
Easy |
简单dp，当前房间偷和不偷两种状态 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291936 |
| 703. Kth Largest Element in a Stream |
Easy |
使用小根堆维护k个值，则第一个元素就是第k大元素 |
https://blog.csdn.net/fuxuemingzhu/article/details/81027116 |
| 345. Reverse Vowels of a String |
Easy |
使用栈进行翻转，或者使用双指针 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291677 |
| 66. Plus One |
Easy |
使用carry表示进位 |
https://blog.csdn.net/fuxuemingzhu/article/details/51346096 |
| 263. Ugly Number |
Easy |
除去2,3,5因子即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/49183961 |
| 35. Search Insert Position |
Easy |
二分查找 |
https://blog.csdn.net/fuxuemingzhu/article/details/70738108 |
| 645. Set Mismatch |
Easy |
使用统计次数或者直接求和计算 |
https://blog.csdn.net/fuxuemingzhu/article/details/79247916 |
| 747. Largest Number At Least Twice of Others |
Easy |
找出最大值，然后弹掉，再找次大值即可。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79188909 |
| 342. Power of Four |
Easy |
递归和迭代 |
https://blog.csdn.net/fuxuemingzhu/article/details/51291091 |
| 724. Find Pivot Index |
Easy |
先求和，在遍历求前半部分的和，找出左边等于右边 |
https://blog.csdn.net/fuxuemingzhu/article/details/79248308 |
| 9. Palindrome Number |
Easy |
可以先翻转成整数，然后判断和原来的是否相等 |
https://blog.csdn.net/fuxuemingzhu/article/details/71334663 |
| 482. License Key Formatting |
Easy |
计算第一个分割的长度，后面都是等长的了 |
https://blog.csdn.net/fuxuemingzhu/article/details/79234075 |
| 1. Two Sum |
Easy |
保存已经出现过的数字的索引，当下次遍历的时候遇到了满足要求的结果，那么既是停止 |
https://blog.csdn.net/fuxuemingzhu/article/details/72465759 |
| 459. Repeated Substring Pattern |
Easy |
判断每个子串重复多次能不能组成原来的串即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/54564801 |
| 849. Maximize Distance to Closest Person |
Easy |
从前向后以及从后向前遍历两次，取最近距离 |
https://blog.csdn.net/fuxuemingzhu/article/details/80643250 |
| 38. Count and Say |
Easy |
统计字符连续出现的次数，并说出来，需要注意最后的一个字符也要添加上去 |
https://blog.csdn.net/fuxuemingzhu/article/details/71618640 |
| 80. Remove Duplicates from Sorted Array II |
Easy |
快指针移动判断和慢指针是否相等，如果不等就换到前面来 |
https://blog.csdn.net/fuxuemingzhu/article/details/82829709 |
| 643. Maximum Average Subarray I |
Easy |
一定注意是长度为k的滑动窗口，注意下标 |
https://blog.csdn.net/fuxuemingzhu/article/details/79248629 |
| 501. Find Mode in Binary Search Tree |
Easy |
如果使用附加空间，可以使用字典保存次数；否则需要遍历两次，判断出现次数。 |
https://blog.csdn.net/fuxuemingzhu/article/details/71124600 |
| 374. Guess Number Higher or Lower |
Easy |
使用二分查找 |
https://blog.csdn.net/fuxuemingzhu/article/details/71516105 |
| 743. Network Delay Time |
Easy |
dijkstra算法 |
https://leetcode.com/problems/network-delay-time/description/ |
| 558. Quad Tree Intersection |
Easy |
递归构造 |
https://blog.csdn.net/fuxuemingzhu/article/details/82356008 |
| 172. Factorial Trailing Zeroes |
Easy |
数有多少个5就行了 |
https://blog.csdn.net/fuxuemingzhu/article/details/51347044 |
| 441. Arranging Coins |
Easy |
二分查找满足条件的层数即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/71330733 |
| 225. Implement Stack using Queues |
Easy |
使用一个队列就能实现栈，每次Push的时候，把队列里的所有元素弹出再放进来就好了。 |
https://blog.csdn.net/fuxuemingzhu/article/details/72598111 |
| 67. Add Binary |
Easy |
使用进位进行模拟 |
ddhttps://blog.csdn.net/fuxuemingzhu/article/details/77341154v |
| 434. Number of Segments in a String |
Easy |
string.split()默认就是按照多个空格分割 |
https://blog.csdn.net/fuxuemingzhu/article/details/71194298 |
| 112. Path Sum |
Easy |
递归和迭代都能满足 |
https://blog.csdn.net/fuxuemingzhu/article/details/71715810 |
| 205. Isomorphic Strings |
Easy |
分别看s到t的映射和t到s的映射是不是一一映射的 |
https://blog.csdn.net/fuxuemingzhu/article/details/72127108 |
| 443. String Compression |
Easy |
使用Pos变量维护应该放到哪个位置，然后一次遍历统计次数就好了 |
https://blog.csdn.net/fuxuemingzhu/article/details/79183289 |
| 303. Range Sum Query - Immutable |
Easy |
保存每个位置的累积和 |
https://blog.csdn.net/fuxuemingzhu/article/details/79253036 |
| 438. Find All Anagrams in a String |
Easy |
滑动窗口，保存等长的子字符串中包含的字符数是否和另外一个相等 |
https://blog.csdn.net/fuxuemingzhu/article/details/79184109 |
| 20. Valid Parentheses |
Easy |
使用栈判断括号是否合法 |
https://blog.csdn.net/fuxuemingzhu/article/details/72366868 |
| 840. Magic Squares In Grid |
Easy |
暴力判断每个9*9的格子是不是满足题意的河图 |
https://blog.csdn.net/fuxuemingzhu/article/details/80473253 |
| 141. Linked List Cycle |
Easy |
走两步走一步，看是否重合 |
https://blog.csdn.net/fuxuemingzhu/article/details/51297249 |
| 203. Remove Linked List Elements |
Easy |
递归解法不好想，但是代码很简单 |
https://blog.csdn.net/fuxuemingzhu/article/details/77340945 |
| 234. Palindrome Linked List |
Easy |
利用一个数组保存所有的数字，然后判断数组是不是回文的。 |
https://blog.csdn.net/fuxuemingzhu/article/details/72597942 |
| 111. Minimum Depth of Binary Tree |
Easy |
DFS/BFS，其实DFS更难 |
https://blog.csdn.net/fuxuemingzhu/article/details/48519035 |
| 290. Word Pattern |
Easy |
一一映射 |
https://blog.csdn.net/fuxuemingzhu/article/details/72528424 |
| 155. Min Stack |
Easy |
使用辅助栈保存最小值 |
https://blog.csdn.net/fuxuemingzhu/article/details/79253237 |
| 219. Contains Duplicate II |
Easy |
使用字典保存出现的位置，当新的元素到来的时候，更新字典 |
https://blog.csdn.net/fuxuemingzhu/article/details/77387169 |
| 941. Valid Mountain Array |
Easy |
两个while就可以了 |
https://blog.csdn.net/fuxuemingzhu/article/details/84206380 |
| 88. Merge Sorted Array |
Easy |
从后向前进行遍历，每次找到大的往后移动 |
https://blog.csdn.net/fuxuemingzhu/article/details/77444695 |
| 914. X of a Kind in a Deck of Cards |
Easy |
需要进行一个遍历，找到是否存在这个分组大小 |
https://blog.csdn.net/fuxuemingzhu/article/details/82914279 |
| 680. Valid Palindrome II |
Easy |
需要用到双指针，先找到第一个不相等的位置，然后去除左边或者右边，判断是否是回文 |
https://blog.csdn.net/fuxuemingzhu/article/details/79252779 |
| 687. Longest Univalue Path |
Easy |
定义的DFS是对过root的单臂进行循环，但是更新的结果是双臂，有点意思 |
https://blog.csdn.net/fuxuemingzhu/article/details/79248926 |
| 14. Longest Common Prefix |
Easy |
遍历最短的子串的每一位，看所有字符串在这一位上是不是相等的 |
https://blog.csdn.net/fuxuemingzhu/article/details/77561186 |
| 686. Repeated String Match |
Easy |
重复NB/NA + 3次，看b是不是在a里 |
https://blog.csdn.net/fuxuemingzhu/article/details/79574835 |
| 122.Best Time to Buy and Sell Stock II |
Easy |
只要每天的比前面一天高，那么就买上并且卖掉即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/70258549 |
| 28. Implement strStr() |
Easy |
循环加切片 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254558 |
| 475. Heaters |
Easy |
找出最临近的距离 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254295 |
| 754. Reach a Number |
Easy |
数学题，非常不喜欢 |
https://blog.csdn.net/fuxuemingzhu/article/details/84556932 |
| 400. Nth Digit |
Easy |
数学计算第多少位 |
https://blog.csdn.net/fuxuemingzhu/article/details/84559975 |
| 69. Sqrt(x) |
Easy |
二分查找或者牛顿法 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254648 |
| 581. Shortest Unsorted Continuous Subarray |
Easy |
先排序，然后比较不等的位置 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254454 |
| 190. Reverse Bits |
Easy |
翻转二进制再转成整数 |
https://blog.csdn.net/fuxuemingzhu/article/details/79254344 |
| 125. Valid Palindrome |
Easy |
过滤掉不是字母的字符，然后判断是不是回文即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79252936 |
| 874. Walking Robot Simulation |
Easy |
模拟整个过程即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/82356556 |
| 532. K-diff Pairs in an Array |
Easy |
找绝对值出现等于k的次数，需要对k进行判断 |
https://blog.csdn.net/fuxuemingzhu/article/details/79255633 |
| 168. Excel Sheet Column Title |
Easy |
需要对26取余，并且做个判断，因为0\26对26取余的结果是一样的 |
https://blog.csdn.net/fuxuemingzhu/article/details/51286857 |
| 189. Rotate Array |
Easy |
可以使用额外数组，也可使用递归原地翻转 |
https://blog.csdn.net/fuxuemingzhu/article/details/79258753 |
| 665. Non-decreasing Array |
Easy |
找到变小的位置，然后和再前面的数字进行判断，看是应该修改当前的还是前面的 |
https://blog.csdn.net/fuxuemingzhu/article/details/79264475 |
| 707. Design Linked List |
Easy |
自己实现链表，挺复杂的。可以使用list进行模拟，方便很多。 |
https://blog.csdn.net/fuxuemingzhu/article/details/81026066 |
| 938. Range Sum of BST |
Medium |
需要根据根节点的值进行判断，邮编和左边需不需要继续寻找 |
https://blog.csdn.net/fuxuemingzhu/article/details/83961263 |
| 807. Max Increase to Keep City Skyline |
Medium |
分别找出行和咧的最大值，把每个位置增长到行列最大值的最小值 |
https://blog.csdn.net/fuxuemingzhu/article/details/79820383 |
| 535. Encode and Decode TinyURL |
Medium |
使用字典完成映射 |
https://blog.csdn.net/fuxuemingzhu |
| 654. Maximum Binary Tree |
Medium |
找到最大值，然后数组切片 |
https://blog.csdn.net/fuxuemingzhu/article/details/79265180 |
| 701. Insert into a Binary Search Tree |
Medium |
递归解法，直接对当前节点进行操作！ |
https://blog.csdn.net/fuxuemingzhu/article/details/82385503 |
| 890. Find and Replace Pattern |
Medium |
判断是不是一一映射 |
https://blog.csdn.net/fuxuemingzhu/article/details/82014687 |
| 921. Minimum Add to Make Parentheses Valid |
Medium |
使用一个栈 |
https://blog.csdn.net/fuxuemingzhu/article/details/83045871 |
| 797. All Paths From Source to Target |
Medium |
回溯法找路径 |
https://blog.csdn.net/fuxuemingzhu/article/details/79624149 |
| 861. Score After Flipping Matrix |
Medium |
把行进行翻转，按列统计1的个数即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/81118328 |
| 894. All Possible Full Binary Trees |
Medium |
使用两种循环遍历可能构成的左子树和右子树，每次构建新的root |
https://blog.csdn.net/fuxuemingzhu/article/details/82084204 |
| 763. Partition Labels |
Medium |
使用字典保存每个字符最后出现的位置，如果一个区间内字符的最后位置的都在一起，那么就添加到结果里 |
https://blog.csdn.net/fuxuemingzhu/article/details/79265829 |
| 419. Battleships in a Board |
Medium |
直接数有多少小岛就行，判断小岛可以使用它的最左上角元素即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79403172 |
| 537. Complex Number Multiplication |
Medium |
复数运算，重点是分割字符串 |
https://blog.csdn.net/fuxuemingzhu/article/details/79266080 |
| 338. Counting Bits |
Medium |
i的二进制1个数等于i/2的二进制个数+i%2 |
https://blog.csdn.net/fuxuemingzhu/article/details/70806676 |
| 885. Spiral Matrix III |
Medium |
保留循环更新步数，很恶心 |
https://blog.csdn.net/fuxuemingzhu/article/details/82389223 |
| 791. Custom Sort String |
Medium |
统计次数，拼接成字符串 |
https://blog.csdn.net/fuxuemingzhu/article/details/79378688 |
| 442. Find All Duplicates in an Array |
Medium |
原地变成负数，如果已经是负数，那么说明出现了两次。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79275549 |
| 355. Design Twitter |
Medium |
使用优先级队列弹出最新的内容 |
https://blog.csdn.net/fuxuemingzhu/article/details/82155420 |
| 841. Keys and Rooms |
Medium |
可以使用DFS和BFS解决 |
https://blog.csdn.net/fuxuemingzhu/article/details/80476862 |
| 406. Queue Reconstruction by Height |
Medium |
先插入长得高的他们不会影响别人，然后在对应位置插入次高的 |
https://blog.csdn.net/fuxuemingzhu/article/details/68486884 |
| 513. Find Bottom Left Tree Value |
Medium |
层次遍历，找出最后一层的第一个节点即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/70161829 |
| 739. Daily Temperatures |
Medium |
使用一个栈，保存每个元素，如果后面的元素比较大，那么就已知出栈操作 |
https://blog.csdn.net/fuxuemingzhu/article/details/79285081 |
| 946. Validate Stack Sequences |
Medium |
使用栈进行模拟，无论如何都把当前的元素弹出，然后和弹出的元素进行比较，相等的话一直弹出 |
https://blog.csdn.net/fuxuemingzhu/article/details/84495797 |
| 515. Find Largest Value in Each Tree Row |
Medium |
遍历每一层，找出最大值即可。 |
https://blog.csdn.net/fuxuemingzhu/article/details/70183314 |
| 540. Single Element in a Sorted Array |
Medium |
可以使用很风骚的二分查找k, |
https://blog.csdn.net/fuxuemingzhu/article/details/79275636 |
| 889. Construct Binary Tree from Preorder and Postorder Traversal |
Medium |
找到后序的倒数第二个元素就是右子树的根节点 |
https://blog.csdn.net/fuxuemingzhu/article/details/82391321 |
| 260. Single Number III |
Medium |
使用异或或者字典解决 |
https://blog.csdn.net/fuxuemingzhu/article/details/79434100 |
| 553. Optimal Division |
Medium |
这个题非常tricky，没意思 |
https://blog.csdn.net/fuxuemingzhu/article/details/79403723 |
| 647. Palindromic Substrings |
Medium |
判断回文，需要判断去掉两头字符之后是否仍然是回文，动态规划 |
https://blog.csdn.net/fuxuemingzhu/article/details/79433960 |
| 695. Max Area of Island |
Medium |
找到岛的数量，这个题可以使用BFS或者DFS的方法 |
https://blog.csdn.net/fuxuemingzhu/article/details/79182435 |
| 856. Score of Parentheses |
Medium |
可以使用栈和递归，这个题很巧妙，是个不错的题目 |
https://blog.csdn.net/fuxuemingzhu/article/details/84956643 |
| 919. Complete Binary Tree Inserter |
Medium |
使用数组保存每个节点的指针，因为是完全二叉树，所以节点位置除以2就得到了它的父亲节点 |
https://blog.csdn.net/fuxuemingzhu/article/details/82958284 |
| 451. Sort Characters By Frequency |
Medium |
根据出现次数排序，然后构建新的字符串即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/79437548 |
| 789. Escape The Ghosts |
Medium |
找出是否存在更小的曼哈顿距离 |
https://blog.csdn.net/fuxuemingzhu/article/details/80480462 |
| 94. Binary Tree Inorder Traversal |
Medium |
中序遍历本身很简单，但是这个递归的写法不好想 |
https://blog.csdn.net/fuxuemingzhu/article/details/79294461 |
| 865. Smallest Subtree with all the Deepest Nodes |
Medium |
定义递归函数：返回<最大深度,最大深度对应的节点> |
https://blog.csdn.net/fuxuemingzhu/article/details/82432130 |
| 508. Most Frequent Subtree Sum |
Medium |
遍历求和，字典统计出现次数最多的所有元素 |
http://www.cnblogs.com/grandyang/p/6481682.html |
| 526. Beautiful Arrangement |
Medium |
经典回溯法，要背会 |
https://blog.csdn.net/fuxuemingzhu/article/details/79431941 |
| 238. Product of Array Except Self |
Medium |
使用两次遍历，分别从左边和右边向中间靠拢 |
https://blog.csdn.net/fuxuemingzhu/article/details/79325534 |
| 712. Minimum ASCII Delete Sum for Two Strings |
Medium |
和LCS很接近的DP题目 |
https://blog.csdn.net/fuxuemingzhu/article/details/79822689 |
| 817. Linked List Components |
Medium |
判断当前节点在set中，但是下一个节点不在即可 |
https://blog.csdn.net/fuxuemingzhu/article/details/80479431 |
| 347. Top K Frequent Elements |
Medium |
使用字典统计次数，使用优先级队列实现排序 |
https://blog.csdn.net/fuxuemingzhu/article/details/79294073 |
| 462. Minimum Moves to Equal Array Elements II |
Medium |
找出中位数，然后求所有数字到中位数的距离和 |
https://blog.csdn.net/fuxuemingzhu/article/details/79437926 |
| 46. Permutations |
Medium |
经典回溯法 |
https://blog.csdn.net/fuxuemingzhu/article/details/79363903 |
| 495. Teemo Attacking |
Medium |
计算每次中毒的开始和结束时间 |
https://blog.csdn.net/fuxuemingzhu/article/details/79438658 |
| 22. Generate Parentheses |
Medium |
经典回溯法 |
https://blog.csdn.net/fuxuemingzhu/article/details/79362373 |
| 529. Minesweeper |
Medium |
扫雷游戏，使用DFS |
https://blog.csdn.net/fuxuemingzhu/article/details/79462285 |
| 667. Beautiful Arrangement II |
Medium |
每次把后面最大数字放到前面来就能增加一种新的差值 |
https://blog.csdn.net/fuxuemingzhu/article/details/79437401 |
| 677. Map Sum Pairs |
Medium |
前缀树的题目，可以背一背 |
https://blog.csdn.net/fuxuemingzhu/article/details/79436619 |
| 547. Friend Circles |
Medium |
并查集的题目 |
https://blog.csdn.net/fuxuemingzhu/article/details/70258103 |
| 565. Array Nesting |
Medium |
一直遍历就好了，使用一个visited数组，但不是回溯。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79460546 |
| 947. Most Stones Removed with Same Row or Column |
Medium |
需要使用并查集，非常考验抽象能力 |
https://blog.csdn.net/fuxuemingzhu/article/details/84500642 |
| 858. Mirror Reflection |
Medium |
镜像反射，需要找规律，分偶数和奇数进行讨论 |
https://blog.csdn.net/fuxuemingzhu/article/details/82432579 |
| 676. Implement Magic Dictionary |
Medium |
找到存不存在汉明间距是1 |
https://blog.csdn.net/fuxuemingzhu/article/details/79447934 |
| 781. Rabbits in Forest |
Medium |
对兔子出现次数进行统计，然后求一个公式。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79457764 |
| 769. Max Chunks To Make Sorted |
Medium |
从左到右遍历一次，时刻保持当前的最大值，如果当前最大值等于索引，那么chunck+1. |
https://blog.csdn.net/fuxuemingzhu/article/details/80482014 |
| 655. Print Binary Tree |
Medium |
先把二叉树构造出来，然后使用类似二分查找左右分治的方法。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79439026 |
| 208. Implement Trie (Prefix Tree) |
Medium |
构造字典树，是个好题，需要背会 |
https://blog.csdn.net/fuxuemingzhu/article/details/79388432 |
| 648. Replace Words |
Medium |
使用字典树或者拉链法求解 |
https://blog.csdn.net/fuxuemingzhu/article/details/79391682 |
| 421. Maximum XOR of Two Numbers in an Array |
Medium |
暴力求解会超时，需要使用异或的性质从最高位开始遍历。或者使用字典树。 |
https://blog.csdn.net/fuxuemingzhu/article/details/79473171 |
| 40. Combination Sum II |
Medium |
经典的回溯法，这个题需要背会 |
https://blog.csdn.net/fuxuemingzhu/article/details/79343638 |