264 - Ugly Number II

2020/06/27

leetcode

Problem

Write a program to find the n-th ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5.

Example:

Input: n = 10
Output: 12
Explanation: 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers.
Note:

1 is typically treated as an ugly number.
n does not exceed 1690.

Solution

class Solution:
    ugly = sorted(2**a * 3**b * 5**c for a in range(32) for b in range(32) for c in range(32))
    def nthUglyNumber(self, n: int) -> int:
        return self.ugly[n-1]