LeetCode-Implement Queue using Stacks-解题报告

原题链接https://leetcode.com/problems/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 onlypush 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).

用栈实现队列，这种题一般都是需要两个栈，当遇到出队或者回去队首元素的时候，将栈1中的元素push到栈2，然后返回栈2的栈顶。

class Queue {public:// Push element x to the back of queue.void push(int x) {one.push(x);}// Removes the element from in front of queue.void pop(void) {if (!two.empty()){two.pop();return;}while (!one.empty()){two.push(one.top());one.pop();}if (!two.empty())two.pop();}// Get the front element.int peek(void) {if (!two.empty())return two.top();while (!one.empty()){two.push(one.top());one.pop();}if (!two.empty())return two.top();}// Return whether the queue is empty.bool empty(void) {return one.empty() && two.empty();}private:stack<int>one;stack<int>two;};