232.用栈实现队列 (二刷)

Author: w2xi

vs-lt/232.用栈实现队列.js

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+/*
+ * @lc app=leetcode.cn id=232 lang=javascript
+ *
+ * [232] 用栈实现队列
+ */
+
+// @lc code=start
+
+var MyQueue = function() {
+  this.stackIn = [];
+  this.stackOut = [];
+};
+
+/** 
+ * @param {number} x
+ * @return {void}
+ */
+MyQueue.prototype.push = function(x) {
+  this.stackIn.push(x);
+};
+
+/**
+ * @return {number}
+ */
+MyQueue.prototype.pop = function() {
+  // in:  [1, 2, 3, 4]
+  // out: []
+  // => 
+  // in:  []
+  // out: [4, 3, 2, 1]
+
+  // 如果输出栈为空, 将输入栈的数据全部导入输出栈
+  if (this.stackOut.length === 0) {
+    let size = this.stackIn.length;
+    while (size--) {
+      this.stackOut.push(this.stackIn.pop());
+    }
+  }
+  return this.stackOut.pop();
+};
+
+/**
+ * @return {number}
+ */
+MyQueue.prototype.peek = function() {
+  // 复用已有方法
+  const result = this.pop();
+  this.stackOut.push(result);
+  return result;
+};
+
+/**
+ * @return {boolean}
+ */
+MyQueue.prototype.empty = function() {
+  return this.stackIn.length === 0 && this.stackOut.length === 0;
+};
+
+/**
+ * Your MyQueue object will be instantiated and called as such:
+ * var obj = new MyQueue()
+ * obj.push(x)
+ * var param_2 = obj.pop()
+ * var param_3 = obj.peek()
+ * var param_4 = obj.empty()
+ */
+// @lc code=end
+