Super Ugly Number

Write a program to find the nth super ugly number.



Super ugly numbers are positive numbers whose all prime factors are in the given prime list
primes of size k. For example, [1, 2, 4, 7, 8, 13, 14, 16, 19, 26, 28, 32]

is the sequence of the first 12 super ugly numbers given primes = [2, 7, 13, 19] of size 4.

Note:
(1) 1 is a super ugly number for any given primes.
(2) The given numbers in primes are in ascending order.
(3) 0 < k &le; 100, 0 < n &le; 106, 0 < primes[i] < 1000.
(4) The nth super ugly number is guaranteed to fit in a 32-bit signed integer.

Credits:Special thanks to @dietpepsi for adding this problem and creating all test cases.

Solution

public class Solution {
        public int nthSuperUglyNumber(int n, int[] primes) {
        if (n <= 0 || primes == null) return -1;
        if (n == 1) return 1;

        int[] times = new int[primes.length];
        int[] ugly = new int[n];
        ugly[0] = 1;

        for (int i = 1; i < n; i++) {
            int min = Integer.MAX_VALUE;
            for(int j = 0; j < primes.length; j ++) {
                min = Math.min(min, primes[j] * ugly[times[j]]);
            }

            ugly[i] = min;
            for(int j = 0; j < primes.length; j ++) {
                if (min == primes[j] * ugly[times[j]]) {
                    times[j] ++;
                }
            }
        }

        return ugly[n-1];
    }

}