leetcode Implement Queue using Stacks

Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

不难，想明白就好，貌似之前看到过这样的题目；一个栈用来存放push的东西，每次需要pop或者peek的时候，再将该栈的所有数据移到另外一个栈里。

 

class Queue {
public:
    stack<int> Squeue1;
    stack<int> Squeue2;
    // Push element x to the back of queue.
    void push(int x) {
        Squeue1.push(x);
    }

    // Removes the element from in front of queue.
    void pop(void) {
            
            int q;
            if(Squeue2.empty()){
            while(!Squeue1.empty()){
            q=Squeue1.top();
            Squeue2.push(q);
            Squeue1.pop();
            }
            }
            Squeue2.pop();
        }
        
  

    // Get the front element.
    int peek(void) {
            int p,q;
            if(Squeue2.empty()){
            while(!Squeue1.empty()){
            q=Squeue1.top();
            Squeue2.push(q);
            Squeue1.pop();
            }
            }
            p=Squeue2.top();
            return p;
    }

    // Return whether the queue is empty.
    bool empty(void) {
        if(Squeue1.empty()&&Squeue2.empty()) return true;
        else return false;
        
    }
};