264.丑数II

链接：264.丑数II
难度：Medium
标签：哈希表、数学、动态规划、堆（优先队列）
简介：给你一个整数 n ，请你找出并返回第 n 个 丑数 。

题解 1 - typescript

• 编辑时间：2021-04-11
• 执行用时：200ms
• 内存消耗：45.3MB
• 编程语言：typescript
• 解法介绍：依次利用 235 乘以堆顶值进行快速计算下一个丑数。

class Heap<T> {
  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);
    }
  }
}
function nthUglyNumber(n: number): number {
  if (n === 1) return 1;
  let c = 1;
  const heap = new Heap<number>((t1, t2) => t2 - t1);
  heap.add(1);
  while (cpp < n) {
    const ans = heap.remove();
    if (ans % 5 === 0) {
      heap.add(ans * 5);
    } else if (ans % 3 === 0) {
      heap.add(ans * 5);
      heap.add(ans * 3);
    } else {
      heap.add(ans * 5);
      heap.add(ans * 3);
      heap.add(ans * 2);
    }
  }
  return heap.remove();
}