LeetCode Super Ugly Number

原题链接在这里：https://leetcode.com/problems/super-ugly-number/

题目：

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.

题解：

与Ugly Number II相似. 

Time Complexity: O(nk). Space: O(n+k). k = primes.length.

AC Java:

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