LeetCode 264 丑数2

编写一个程序，找出第 n 个丑数。

丑数就是质因数只包含 2, 3, 5 的正整数。

两种方法，堆和动态规划

动态规划：

class Solution:
    def nthUglyNumber(self, n: int) -> int:
        i2, i3, i5 = 0, 0, 0
        arr = [1]
        for j in range(1, n):
            val = min(arr[i2] * 2, arr[i3] * 3, arr[i5] * 5)
            arr.append(val)
            if val == arr[i2] * 2:
                i2 += 1
            if val == arr[i3] * 3:
                i3 += 1
            if val == arr[i5] * 5:
                i5 += 1
        return arr[n - 1]

堆：

import heapq


class Solution:
    def nthUglyNumber(self, n: int) -> int:
        """
        因数中只包含2,3,5
        :param n:
        :return:
        """
        list1 = [1]
        set1 = set()
        cnt = 0
        while list1:
            val = heapq.heappop(list1)
            cnt += 1
            if cnt == n:
                return val
            for prime in {2, 3, 5}:
                if val * prime not in set1:
                    heapq.heappush(list1, val * prime)
                    set1.add(val * prime)
        return list1[0]