LeetCode 232. 用栈实现队列
题目描述:
请你仅使用两个栈实现先入先出队列。队列应当支持一般队列支持的所有操作(push
、pop
、peek
、empty
):
实现 MyQueue
类:
void push(int x)
将元素 x 推到队列的末尾int pop()
从队列的开头移除并返回元素int peek()
返回队列开头的元素boolean empty()
如果队列为空,返回 true
;否则,返回 false
说明:
push to top
, peek/pop from top
, size
, 和 is empty
操作是合法的。示例 1:
输入:
["MyQueue", "push", "push", "peek", "pop", "empty"]
[[], [1], [2], [], [], []]
输出:
[null, null, null, 1, 1, false]
解释:
MyQueue myQueue = new MyQueue();
myQueue.push(1); // queue is: [1]
myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
myQueue.peek(); // return 1
myQueue.pop(); // return 1, queue is [2]
myQueue.empty(); // return false
解题思路
解法:
写法
/**
* Initialize your data structure here.
*/
var MyQueue = function() {
this.arr = [];
};
/**
* Push element x to the back of queue.
* @param {number} x
* @return {void}
*/
MyQueue.prototype.push = function(x) {
// this.arr.push(x);
this.arr[this.arr.length] = x
};
/**
* Removes the element from in front of queue and returns that element.
* @return {number}
*/
MyQueue.prototype.pop = function() {
// return this.arr.shift() ;
let [a, ...newArr] = this.arr;
this.arr = newArr;
return a;
};
/**
* Get the front element.
* @return {number}
*/
MyQueue.prototype.peek = function() {
return this.arr[0];
};
/**
* Returns whether the queue is empty.
* @return {boolean}
*/
MyQueue.prototype.empty = function() {
if(this.arr.length == 0) return true;
return false;
};
LeetCode 225. 用队列实现栈
题目描述:
请你仅使用两个队列实现一个后入先出(LIFO)的栈,并支持普通栈的全部四种操作(push
、top
、pop
和 empty
)。
实现 MyStack
类:
void push(int x)
将元素 x 压入栈顶。int pop()
移除并返回栈顶元素。int top()
返回栈顶元素。boolean empty()
如果栈是空的,返回 true
;否则,返回 false
。注意:
push to back
、peek/pop from front
、size
和 is empty
这些操作。示例 1:
输入:
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
输出:
[null, null, null, 2, 2, false]
解释:
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // 返回 2
myStack.pop(); // 返回 2
myStack.empty(); // 返回 False
解题思路
解法:
写法
/**
* Initialize your data structure here.
*/
var MyStack = function() {
this.queue = [];
this.size = 0;
};
/**
* Push element x onto stack.
* @param {number} x
* @return {void}
*/
MyStack.prototype.push = function(x) {
this.queue.push(x);
this.size++;
};
/**
* Removes the element on top of the stack and returns that element.
* @return {number}
*/
MyStack.prototype.pop = function() {
const tempQueue = [];
// 暂时保存队列的前n-1个元素
for(let i = 0; i < this.size - 1; i++) {
tempQueue.push(this.queue.shift());
}
// 取出最晚进入队列的第n个元素,原队列已空,新队列剩下n-1个元素
const val = this.queue.shift();
this.queue = tempQueue;
this.size--;
return val;
};
/**
* Get the top element.
* @return {number}
*/
MyStack.prototype.top = function() {
const tempQueue = [];
for(let i = 0; i < this.size - 1; i++) {
tempQueue.push(this.queue.shift());
}
const val = this.queue.shift();
this.queue = tempQueue;
this.queue.push(val);
return val;
};
/**
* Returns whether the stack is empty.
* @return {boolean}
*/
MyStack.prototype.empty = function() {
return !this.size;
};