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目录
14 最长公共前缀 Longest Common Prefix
21 合并两个有序链表 Merge Two Sorted Lists
26 删除排序数组中的重复选项 Remove Duplicates from Sorted Array
28 实现strStr() Implement strStr()
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1 两数之和 Two Sum
def twoSum1(nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
d = {}
for i in range(len(nums)):
if target - nums[i] in d:
return [d[target - nums[i]], i]
d[nums[i]] = i
def twoSum2(nums, target):
"""
:type nums: List[int]
:type target: int
:rtype: List[int]
"""
d = {}
for i, num in enumerate(nums):
if target - num in d:
return [d[target - num], i]
d[num] = i
7 整数反转 Reverse Integer
def reverse1(x):
"""
:type x: int
:rtype: int
"""
# -214783648 ~ 214783647
num = 0
a = abs(x)
while(a != 0):
temp = a % 10
num = num * 10 + temp
a = int(a/10) # 使用a//10结果不对
if x > 0 and num < 0x7fffffff:
return num
elif x < 0 and num <= 0x7fffffff:
return -num
else:
return 0
def reverse2(x):
"""
:type x: int
:rtype: int
"""
sign = x < 0 and -1 or 1
x = abs(x)
ans = 0
while(x):
ans = ans * 10 + x % 10
x = int(x/10)
return sign * ans if ans < 0x7fffffff else 09 回文数 Palindrome Number
def isPalindrome1(x):
if x < 0:
return False
else:
s = str(x)
return s == s[::-1]
def isPalindrome2(x):
z = x
y = 0
while x > 0:
y = y * 10 + x % 10
x = int(x/10)
return z == y13 罗马数字转整数 Roman to Integer
def romanToInt1(s):
# 思路：把字符串中符合特殊情况的挑出来
a = {"IV": 4, "IX": 9, "XL": 40, "XC": 90, "CD": 400, "CM": 900}
d = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
n = 0
e = []
for i in range(len(s) - 1):
c = s[i] + s[i+1]
if c in a.keys():
n += a[c]
e.append(i)
e.append(i+1)
for i in range(len(s)):
if i not in e:
n += d[s[i]]
return n
def romanToInt2(s):
# 思路：找到规律，如果字符串后一个比前一个大则减前一个的值
d = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
ans = 0
for i in range(len(s) - 1):
c = s[i]
cafter = s[i + 1]
if d[c] < d[cafter]:
ans -= d[c]
else:
ans += d[c]
ans += d[s[-1]]
return ans
def romanToInt3(s):
# 思路: 都加，如果后面大于前面则减去两个前面
d = {"I": 1, "V": 5, "X": 10, "L": 50, "C": 100, "D": 500, "M": 1000}
result = 0
for i in range(len(s)):
if i > 0 and d[s[i]] > d[s[i-1]]:
result += d[s[i]] - 2 * d[s[i-1]]
else:
result += d[s[i]]
return result14 最长公共前缀 Longest Common Prefix
def longestCommonPrefix1(strs):
result = ''
if len(strs) == 0:
return result
a, minstr = 0, min(strs, key=len)
for ch in minstr:
for i in range(1, len(strs)):
if strs[i][a] != ch:
return result
a, result = a + 1, result + ch
return result
def longestCommonPrefix2(strs):
if len(strs) == 0:
return ""
i = 0
j = 0
end = 0
while j < len(strs) and i < len(strs[j]):
if j == 0:
char = strs[j][i]
else:
if strs[j][i] != char:
break
if j == len(strs) - 1:
i += 1
j = 0
end += 1
else:
j += 1
return strs[j][:end]
def longestCommonPrefix3(strs):
"""
通过zip将每个字符串的字母按顺序放入一个元组中：
zip("abc", "abd")
[(a, b), (a, b), (c, d)]
再把元组变为集合即可消去重复元素，所以当集合长度为1时，说明所有字符串在这个位置的字母相等
"""
res = ""
if not strs:
return ""
for each in zip(*strs):
if len(set(each)) == 1:
res += each[0]
else:
return res
return res
def longestCommonPrefix4(strs):
if not strs:
return ""
for i in range(len(strs[0])):
for string in strs[1:]:
if i >= len(string) or string[i] != strs[0][i]:
return strs[0][:i]
return strs[0]20 有效的括号 Valid Parentheses
def isValid1(s):
"""
循环搜索()[]{}并删掉，最后剩余空字符串则为True
"""
k = ["[]", "{}", "()"]
while(s != ""):
n = 0
for i in range(3):
a = s.find(k[i])
if a >= 0:
s = s[:a] + s[a+2:]
print(s)
else:
n += 1
if n == 3:
return False
return True
def isValid2(s):
"""
从头开始检索如果遇到()[]{}就先加上再减去，如果最后为空列表则为True
"""
stack = []
d = ["()", "[]", "{}"]
for i in range(len(s)):
stack.append(s[i])
if len(stack) >= 2 and stack[-2]+stack[-1] in d:
stack.pop()
stack.pop()
return len(stack) == 0
def isValid3(s):
stack = []
lookup = {"(": ")", "{": "}", "[": "]"}
for parenthese in s:
if parenthese in lookup:
stack.append(parenthese)
elif len(stack) == 0 or lookup[stack.pop()] != parenthese:
return False
return len(stack) == 021 合并两个有序链表 Merge Two Sorted Lists
def mergeTwoLists(l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
head = dummy = ListNode(-1)
while l1 and l2:
if l1.val < l2.val:
head.next = l1
l1 = l1.next
else:
head.next = l2
l2 = l2.next
head = head.next
head.next = l1 or l2
return dummy.next
def initLink(data): # 创建新链表
a = ListNode(data[0])
p = a
# 逐个为 data 内的数据创建结点, 建立链表
for i in data[1:]:
node = ListNode(i)
p.next = node
p = p.next
p.next = None
return a
def prtLink(link): # 打印链表
a = []
while link is not None:
a.append(link.val)
link = link.next
print(a)
l1 = initLink([1, 2, 3])
prtLink(l1)
l2 = initLink([1, 3, 4])
prtLink(l2)
l3 = mergeTwoLists(l1, l2)
prtLink(l3)26 删除排序数组中的重复选项 Remove Duplicates from Sorted Array
def removeDuplicates1(nums):
s = set(nums)
nums[:] = []
for i in range(len(s)):
nums.append(sorted(list(s))[i])
return len(nums)
def removeDuplicates2(nums):
if len(nums) <= 1:
return len(nums)
slow = 0
for i in range(1, len(nums)):
if nums[i] != nums[slow]:
slow += 1
nums[slow] = nums[i]
return slow + 1
def removeDuplicates3(nums):
n = 1
if len(nums) > 0:
for num in range(1, len(nums)):
if nums[num] != nums[num-1]:
nums[n] = nums[num]
n += 1
else:
n = 0
return n27 移除元素 Remove Element
def removeElement1(nums, val):
while(1):
try:
nums.remove(val)
except ValueError:
break
return len(nums)
def removeElement2(nums, val):
i = 0
while i < len(nums):
if nums[i] == val:
del nums[i]
else:
i += 1
return len(nums)28 实现strStr() Implement strStr()
def strStr1(haystack, needle):
return haystack.find(needle)
def strStr2(haystack, needle):
try:
n = haystack.index(needle)
except ValueError:
n = -1
return n
def strStr3(haystack, needle):
for i in range(0, len(haystack) - len(needle) + 1):
if haystack[i:i+len(needle)] == needle:
return i
return -1