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.
Notes:
- You must use only standard operations of a queue -- which means only
push to back,peek/pop from front,size, andis emptyoperations are valid. - Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
- You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).
用队列实现栈的功能
C++（2ms）：
1 class MyStack { 2 public: 3 queue<int> q ; 4 /** Initialize your data structure here. */ 5 MyStack() { 6 7 } 8 9 /** Push element x onto stack. */ 10 void push(int x) { 11 q.push(x) ; 12 for(int i = 0 ; i < q.size()-1 ; i++){ 13 q.push(q.front()) ; 14 q.pop() ; 15 } 16 } 17 18 /** Removes the element on top of the stack and returns that element. */ 19 int pop() { 20 int t = q.front() ; 21 q.pop() ; 22 return t ; 23 } 24 25 /** Get the top element. */ 26 int top() { 27 return q.front() ; 28 } 29 30 /** Returns whether the stack is empty. */ 31 bool empty() { 32 return q.empty() ; 33 } 34 }; 35 36 /** 37 * Your MyStack object will be instantiated and called as such: 38 * MyStack obj = new MyStack(); 39 * obj.push(x); 40 * int param_2 = obj.pop(); 41 * int param_3 = obj.top(); 42 * bool param_4 = obj.empty(); 43 */
