js练习-两个栈实现队列

题

现在有个Q队列和栈A，栈B，栈只有两个方法，push()和pop(), 队列也只有两个方法，push()和pull()，队列的进和出都只能通过A和B的push和pop实现。

// 大概举个例子
const Q = {

    a = new A(),
    b = new B(),

    push() {

    },

    pull() {

    }
}

解

const Q = {
  a: [], // 先放
  b: [], // 后放

  push(value) {
    const lengthA = this.a.length;
    const lengthB = this.b.length;
    if (lengthA === lengthB) {
      this.a.push(value);
    } else {
      this.b.push(value);
    }
    return lengthA + lengthB + 1;
  },

  pull() {
    const lengthA = this.a.length;
    if (!lengthA) return undefined;

    const func = (popArray, pushArray, forLength) => {
      for (let i = 0; i < forLength; i++) {
        const value = popArray.pop();
        pushArray.push(value);
      }
    };

    func(this.a, this.b, lengthA - 1);
    const result = this.a.pop();
    func(this.b, this.a, lengthA - 1);

    const { a } = this;
    this.a = this.b;
    this.b = a;

    return result;
  },
};
Q.push('a');
Q.push('b');
Q.push('c');
Q.pull(); // a
Q.pull(); // b
Q.pull(); // c