232. 用栈实现队列

请你仅使用两个栈实现先入先出队列。

解题思路

var MyQueue = function () {
  this.stack1 = [] // support push() and pop()
  this.stack2 = []
}

/**
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function (x) {
  if (this.stack2.length) {
    while (this.stack2.length) {
      this.stack1.push(this.stack2.pop())
    }
  }

  this.stack1.push(x)
}

/**
 * @return {number}
 */
MyQueue.prototype.pop = function () {
  if (this.stack1.length) {
    this.stack2.length = 0

    // equal to call empty()
    while (this.stack1.length) {
      this.stack2.push(this.stack1.pop())
    }
  }

  const v = this.stack2.pop()

  return v
}

/**
 * @return {number}
 */
MyQueue.prototype.peek = function () {
  if (this.stack1.length) {
    this.stack2.length = 0

    while (this.stack1.length) {
      this.stack2.push(this.stack1.pop())
    }
  }

  // equal to call peek()
  return this.stack2[this.stack2.length - 1]
}

/**
 * @return {boolean}
 */
MyQueue.prototype.empty = function () {
  return !(this.stack1.length || this.stack2.length)
}

参考

-232. 用栈实现队列 - 力扣（LeetCode） (opens new window)