414.第三大的数

链接：414.第三大的数
难度：Easy
标签：数组、排序
简介：给定两个整数，分别表示分数的分子 numerator 和分母 denominator，以 字符串形式返回小数 。

题解 1 - typescript

• 编辑时间：2021-10-06
• 执行用时：84ms
• 内存消耗：40.7MB
• 编程语言：typescript
• 解法介绍：堆。

class Heap<T = number> {
  private arr: T[] = [];
  get isEmpty() {
    return this.size === 0;
  }
  get size() {
    return this.arr.length;
  }
  get top() {
    return this.arr[0];
  }
  constructor(private compare: (t1: T, t2: T) => number) {}
  add(num: T): void {
    this.arr.push(num);
    this.shiftUp(this.size - 1);
  }
  remove(): T {
    const num = this.arr.shift()!;
    if (this.size) {
      this.arr.unshift(this.arr.pop()!);
      this.shiftDown(0);
    }
    return num;
  }
  private shiftUp(index: number): void {
    if (index === 0) return;
    const parentIndex = (index - 1) >> 1;
    if (this.compare(this.arr[index], this.arr[parentIndex]) > 0) {
      [this.arr[index], this.arr[parentIndex]] = [this.arr[parentIndex], this.arr[index]];
      this.shiftUp(parentIndex);
    }
  }
  private shiftDown(index: number): void {
    let childrenIndex = index * 2 + 1;
    if (childrenIndex > this.size - 1) return;
    if (
      childrenIndex + 1 <= this.size - 1 &&
      this.compare(this.arr[childrenIndex + 1], this.arr[childrenIndex]) > 0
    ) {
      childrenIndex++;
    }
    if (this.compare(this.arr[childrenIndex], this.arr[index]) > 0) {
      [this.arr[childrenIndex], this.arr[index]] = [this.arr[index], this.arr[childrenIndex]];
      this.shiftDown(childrenIndex);
    }
  }
  *[Symbol.iterator](): IterableIterator<T> {
    for (const t of this.arr) {
      yield t;
    }
  }
}
function thirdMax(nums: number[]): number {
  const heap = new Heap((t1, t2) => t1 - t2);
  [...new Set(nums)].forEach(num => heap.add(num));
  if (heap.size < 3) return heap.remove();
  let ans = 0;
  for (let i = 0; i < 3; i++) ans = heap.remove();
  return ans;
}

题解 2 - typescript

• 编辑时间：2021-10-06
• 执行用时：80ms
• 内存消耗：40.1MB
• 编程语言：typescript
• 解法介绍：排序。

function thirdMax(nums: number[]): number {
  nums = [...new Set(nums)].sort((a, b) => b - a);
  return nums[2] ?? nums[0];
}