1307. Ugly Number III

Medium
Math
Binary Search
Combinatorics
Number Theory

Description

An ugly number is a positive integer that is divisible by a, b, or c.

Given four integers n, a, b, and c, return the nth ugly number.

 

Example 1:

Input: n = 3, a = 2, b = 3, c = 5
Output: 4
Explanation: The ugly numbers are 2, 3, 4, 5, 6, 8, 9, 10... The 3rd is 4.

Example 2:

Input: n = 4, a = 2, b = 3, c = 4
Output: 6
Explanation: The ugly numbers are 2, 3, 4, 6, 8, 9, 10, 12... The 4th is 6.

Example 3:

Input: n = 5, a = 2, b = 11, c = 13
Output: 10
Explanation: The ugly numbers are 2, 4, 6, 8, 10, 11, 12, 13... The 5th is 10.

 

Constraints:

  • 1 <= n, a, b, c <= 109
  • 1 <= a * b * c <= 1018
  • It is guaranteed that the result will be in range [1, 2 * 109].

Hints

Hint 1
Write a function f(k) to determine how many ugly numbers smaller than k. As f(k) is non-decreasing, try binary search.
Hint 2
Find all ugly numbers in [1, LCM(a, b, c)] (LCM is Least Common Multiple). Use inclusion-exclusion principle to expand the result.

Similar Questions

Statistics

Acceptance
31.1%
Submissions
135,077
Accepted
41,944