[LeetCode][JavaScript]Implement Stack using Queues

標籤：

Implement Stack using Queues

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, and is empty operations 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).

 

Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.

https://leetcode.com/problems/implement-stack-using-queues/

 

 

    用隊列類比棧。只能用隊列的入隊，出隊，長度和是否為空白四個功能。也就是js數組的push(),shift(),length,length===0。 兩個隊列倒來倒去。入棧操作就是找到不為空白的隊列，入隊。出棧和查看棧頂元素的操作是一樣的，把不為空白的那個隊列，除了最後一個元素的其他所有元素都倒到另一個裡去。棧是否為空白就是兩個隊列是否都為空白。 

 1 /** 2  * @constructor 3  */ 4 var Stack = function() { 5     this.queueA = []; 6     this.queueB = []; 7 }; 8  9 /**10  * @param {number} x11  * @returns {void}12  */13 Stack.prototype.push = function(x) {14     if(this.queueA.length !== 0){15         this.queueA.push(x);16     }else{17         this.queueB.push(x);18     }19 };20 21 Stack.prototype.moveAToB = function() {22     if(this.queueB.length !== 0){23         var tmp = this.queueA;24         this.queueA = this.queueB;25         this.queueB = tmp;26     }27     var len = this.queueA.length;28     for(var i = 0; i < len - 1; i++){29         var queuePeek = this.queueA.shift();30         this.queueB.push(queuePeek);31     }32 };33 34 /**35  * @returns {void}36  */37 Stack.prototype.pop = function() {38     this.moveAToB();39     this.queueA.shift();40 };41 42 /**43  * @returns {number}44  */45 Stack.prototype.top = function() {46     this.moveAToB();47     var stackTop = this.queueA.shift();48     this.queueB.push(stackTop);49     return stackTop;50 };51 52 /**53  * @returns {boolean}54  */55 Stack.prototype.empty = function() {56     if(this.queueA.length === 0 && this.queueB.length === 0){57         return true;58     }59     return false;60 };

 

 

     

[LeetCode][JavaScript]Implement Stack using Queues