27. Remove Element
Given an array nums and a value val, remove all instances of that value in-place and return the new length.
Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.
The order of elements can be changed. It doesn’t matter what you leave beyond the new length.
Example 1:
Given nums = [3,2,2,3], val = 3,
Your function should return length = 2, with the first two elements of nums being 2.
It doesn’t matter what you leave beyond the returned length.
JAVA
class Solution {
public int removeElement(int[] nums, int val) {
int j=0;
for(int i=0;i<nums.length;i++)
{
if(nums[i]!=val)
{
nums[j]=nums[i];
j++;
}
}
return j;
}
}
C++
class Solution {
public:
int removeElement(vector<int>& nums, int val) {
int j=0;
for(int i=0;i<nums.size();i++)
{
if(nums[i]!=val)
{
nums[j]=nums[i];
j++;
}
}
return j;
}
};
225. Implement Stack using Queues
Implement the following operations of a stack using queues.
push(x) – Push element x onto stack.
pop() – Removes the element on top of the stack.
top() – Get the top element.
empty() – Return whether the stack is empty.
Example:
MyStack stack = new MyStack();
stack.push(1);
stack.push(2);
stack.top(); // returns 2
stack.pop(); // returns 2
stack.empty(); // returns false
用队列来实现栈
C++
class MyStack {
public:
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
q.push(x);
for(int i=0;i<(int)q.size()-1;i++)
{
q.push(q.front());
q.pop();
}
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
int x = q.front(); q.pop();
return x;
}
/** Get the top element. */
int top() {
return q.front();
}
/** Returns whether the stack is empty. */
bool empty() {
return q.empty();
}
private:
queue<int> q;
};
/**
* Your MyStack object will be instantiated and called as such:
* MyStack* obj = new MyStack();
* obj->push(x);
* int param_2 = obj->pop();
* int param_3 = obj->top();
* bool param_4 = obj->empty();
*/
933. Number of Recent Calls
Write a class RecentCounter to count recent requests.
It has only one method: ping(int t), where t represents some time in milliseconds.
Return the number of pings that have been made from 3000 milliseconds ago until now.
Any ping with time in [t - 3000, t] will count, including the current ping.
It is guaranteed that every call to ping uses a strictly larger value of t than before.
Example 1:
Input: inputs = [“RecentCounter”,“ping”,“ping”,“ping”,“ping”], inputs = [[],[1],[100],[3001],[3002]]
Output: [null,1,2,3,3]
写一个RecentCounter类来计算最近的请求。
看不懂（为了应付考试）
JAVA
class RecentCounter {
TreeSet<Integer> ts;
public RecentCounter() {
ts=new TreeSet<>();
}
public int ping(int t) {
ts.add(t);
return ts.tailSet(t-3000).size();
}
}