Inverse Factorial
The factorial of a number n is defined as n! = n * (n - 1) * (n - 2) * ... * 1.
Given a positive integer a, return n such that n! = a. If there is no integer n that is a factorial, then return -1.
Constraints
0 < a < 2 ** 31
https://binarysearch.com/problems/Inverse-Factorial
ExamplesPermalink
Example 1Permalink
Input
- a =
6
Output
- answer =
3
Explanation
3! = 6
Example 2Permalink
Input
- a =
10
Output
- answer =
-1
Explanation
10 is not any integer factorial.
SolutionPermalink
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| int solve(int a) | |
| { | |
| if (a <= 0) | |
| return -1; | |
| int divisor = 1; | |
| while (a > 1 && a % divisor == 0) | |
| { | |
| a /= divisor; | |
| divisor++; | |
| } | |
| return a == 1 ? divisor - 1 : -1; | |
| } |
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