Leetcode-232-implement Queue using Stacks

Implement Queue using Stacks

Implement the following operations of a queue using stacks.

• Push (x)--push element x to the back of the queue.
• Pop ()--Removes the element from in front of the 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 < Code style= "Font-family:menlo,monaco,consolas, ' Courier New ', monospace; font-size:12.6000003814697px; PADDING:2PX 4px; Color:rgb (199,37,78); Background-color:rgb (249,242,244) ">push to top ,  peek/pop from top ,  size , And is empty  operations is valid.
• Depending on your language, stack may is not supported natively. You could simulate a stack by using a list or deque (double-ended queue), as long as if you have standard operations of a s Tack.
• You may assume this all operations is valid (for example, no pop or peek operations would be called on an empty queue).

Implement queues with stacks.

Two stacks to implement a queue.

Class Queue {public:    stack<int>s1,s2;    Push element x to the back of the queue.    void push (int x) {        s1.push (x);    }    Removes the element from in front of the queue.    void pop (void) {        while (!s1.empty ()) {            S2.push (s1.top ());            S1.pop ();        }        S2.pop ();        while (!s2.empty ()) {            S1.push (s2.top ());            S2.pop ();        }    }    Get the front element.    int peek (void) {        while (!s1.empty ()) {            S2.push (s1.top ());            S1.pop ();        }        int x = S2.top ();//Fetch stack top element while        (!s2.empty ()) {            S1.push (s2.top ());            S2.pop ();        }                return x;    }    Return whether the queue is empty.    bool Empty (void) {        return s1.empty ();    }};

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Leetcode-232-implement Queue using Stacks