Leetcode no. 313

313. 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 ≤ 100, 0 < n ≤ 106, 0 < primes[i] < 1000.

public class Solution {
    public int nthSuperUglyNumber(int n, int[] primes) {
        int[] ugly= new int[n];
        int[] index= new int[primes.length]; //对于第j个prime 乘以第index[j]个ugly
        ugly[0]= 1;
        for (int i = 1; i < n; i++) {
            ugly[i]= Integer.MAX_VALUE;
            //find next
            for (int j = 0; j < primes.length; j++) { //对于每个prime都要试最小的那个ugly(index[j])
                ugly[i]= Math.min(ugly[i], primes[j]* ugly[index[j]]);
            }
            //skip duplicate
            for (int j = 0; j < primes.length; j++) {
                while (primes[j]* ugly[index[j]] <= ugly[i]) index[j]++;
            }
        }
        return ugly[n-1];
    }
}