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.

Analysis

• Can use same method from ugly number II, only difference is change of basic prime numbers.
• Use List for uglylist can not pass OJ, time limit exceed. Change to int[], pass OJ. list is dynamic, use less room, must be use more time...

Code

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

Reference

Ugly Number II