An ugly number is a positive integer whose prime factors are limited to 2, 3, and 5.
Given an integer n, return the nth ugly number.
Example 1:
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.
Example 2:
Input: n = 1
Output: 1
Explanation: 1 has no prime factors, therefore all of its prime factors are limited to 2, 3, and 5.
Constraints:
-
1 <= n <= 1690
SOLUTION:
import heapq
class Solution:
def nthUglyNumber(self, n: int) -> int:
uglies = [1]
uglySet = {1}
while len(uglies) < n * 10:
for num in uglies[:]:
for k in [2, 3, 5]:
p = num * k
if p not in uglySet:
heapq.heappush(uglies, p)
uglySet.add(p)
return heapq.nsmallest(n, uglies)[n - 1]
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