牛客网刷题：丑数

解题思路：https://blog.csdn.net/weixin_37251044/article/details/89288546

# -*- coding:utf-8 -*-
class Solution:
    def GetUglyNumber_Solution(self, index):
        # write code here
        if index == 0:
            return 0 
        res = [1]
        t2 = t3 = t5 = 0
        cnt = 1
        while cnt < index:
            res.append(min(res[t2]*2, res[t3]*3, res[t5]*5))
            if res[-1] == res[t2]*2:
                t2 += 1
            if res[-1] == res[t3]*3:
                t3 += 1
            if res[-1] == res[t5]*5:
                t5 += 1
            cnt += 1
        return res[cnt-1]