[leetcode] 313. Super Ugly Number 解题报告

题目链接：https://leetcode.com/problems/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.

思路：和ugly number的思路差不多，都是保存给的几个素数在ugly序列中的位置，代表那个位置的ugly number乘以那个素数大于当前的数，这样每次就可以比较得到当前哪个相乘可以得到最小的ugly number.

代码如下：

class Solution {
public:
    int nthSuperUglyNumber(int n, vector<int>& primes) {
        vector<int> index(primes.size(), 0), vec{1};
        while(--n > 0)
        {
            int Min = INT_MAX, len = primes.size();
            for(int i =0; i < len; i++) Min = min(vec[index[i]] * primes[i] , Min);
            vec.push_back(Min);
            for(int i = 0; i < len; i++)
                while(primes[i] * vec[index[i]] <= Min) index[i]++;
        }
        return vec.back();
    }
};