[LeetCode][JavaScript]Implement Queue using Stacks

標籤：

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).

 https://leetcode.com/problems/implement-queue-using-stacks/     2個棧實現隊列。棧1為主，棧2為輔。push操作，先把棧2所有的元素都倒入棧1，然後對棧1壓桟。pop和peek操作，如果棧2為空白，就把棧1所有元素都倒入棧2，然後對棧2出桟。

 1 /** 2  * @constructor 3  */ 4 var Queue = function() { 5     this.stack1 = []; 6     this.stack2 = []; 7 }; 8  9 /**10  * @param {number} x11  * @returns {void}12  */13 Queue.prototype.push = function(x) {14     var len = this.stack2.length;15     while(len--){16         this.stack1.push(this.stack2.pop());17     }18     this.stack1.push(x);19 };20 21 /**22  * @returns {void}23  */24 Queue.prototype.pop = function() {25     if(this.stack2.length === 0){26         var len = this.stack1.length;27         while(len--){28             this.stack2.push(this.stack1.pop());29         }30     }31     return this.stack2.pop();32 };33 34 /**35  * @returns {number}36  */37 Queue.prototype.peek = function() {38     if(this.stack2.length === 0){39         var len = this.stack1.length;40         while(len--){41             this.stack2.push(this.stack1.pop());42         }43     }44     return this.stack2[this.stack2.length - 1];45 };46 47 /**48  * @returns {boolean}49  */50 Queue.prototype.empty = function() {51     if(this.stack1.length === 0 && this.stack2.length === 0){52         return true;53     }54     return false;55 };

 

 

[LeetCode][JavaScript]Implement Queue using Stacks