313. Super Ugly Number - jiejackyzhang/leetcode-note GitHub Wiki

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.

解题思路与264. Ugly Number II类似。 只是从2，3，5扩展为更为一般化的一个primes数组。

public class Solution {
    public int nthSuperUglyNumber(int n, int[] primes) {
        int[] ugly = new int[n];
        ugly[0] = 1;
        int[] idx = new int[primes.length];
        int i = 1;
        while(i < n) {
            ugly[i] = Integer.MAX_VALUE;
            for(int j = 0; j < primes.length; j++) {
                if(ugly[idx[j]] * primes[j] == ugly[i-1]) {
                    idx[j]++;
                }
                ugly[i] = Math.min(ugly[i], ugly[idx[j]] * primes[j]);
            }
            i++;
        }
        return ugly[n-1];
    }
}