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).
使用隊列來模仿棧：
使用隊列頭來模擬棧頂辣往，這樣pop和top方法都是直接就取到兔院。
至于push，我們可以在放進新元素的時候把隊列中排在這個元素前面的元素一個一個取出來再放回這個隊列站削。
/**
* @constructor
*/
var Stack = function() {
this.q1 = [];
};
/**
* @param {number} x
* @returns {void}
*/
Stack.prototype.push = function(x) {
this.q1.push(x);
var num = this.q1.length-1;
for (var i = 0; i<num; i++) {
this.q1.push(this.q1.shift());
}
};
/**
* @returns {void}
*/
Stack.prototype.pop = function() {
return this.q1.shift();
};
/**
* @returns {number}
*/
Stack.prototype.top = function() {
return this.q1[0];
};
/**
* @returns {boolean}
*/
Stack.prototype.empty = function() {
if (this.q1.length===0)
return true;
else
return false;
};
