[LeetCode 313] Super Ugly Number

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本文介绍了一种算法，用于找到序列中的第N个超丑数。超丑数是指其所有质因数都在给定质数列表中的正整数。文章通过一个具体的例子展示了如何实现这一算法。

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 int nthSuperUglyNumber(int n, int[] primes) {
        int len = primes.length;
        int[] res = new int[n];
        int[] index = new int[len];
        res[0] =1;
        if(n<=1) return res[0];
        for(int i=1;i<n;i++) {
            int num = Integer.MAX_VALUE;
            for(int j=0;j<len;j++) {
                num = Math.min(num, primes[j] * res[index[j]]);
            }
            res[i] = num;
            for(int j=0;j<len;j++) {
                if(res[i] % primes[j]==0) index[j]++;
            }
        }
        return res[n-1];
    }