leetcode刷题， 总结，记录，备忘 232

leetcode232

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).

很简单的一题，尾部插入那边，使用2个stack来回倒就行2了，so easy

class Queue {
public:
    // Push element x to the back of queue.
    void push(int x) {
        int temp;
        while (s.size())
        {
            t.push(s.top());
            s.pop();
        }
        s.push(x);
       while (t.size())
       {
           temp = t.top();
           t.pop();
           s.push(temp);
       }
    }

    // Removes the element from in front of queue.
    void pop(void) {
        s.pop();
    }

    // Get the front element.
    int peek(void) {
        return s.top();
    }

    // Return whether the queue is empty.
    bool empty(void) {
        return s.size() == 0;
    }
    stack<int> s;
    stack<int> t;
};