［LeetCode］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.

用一个指针数组来记录每个质数乘积的次数，用另一个数字存储解。

时间复杂度O(nk)，空间O(n)+O(k)

class Solution {
public:
    int nthSuperUglyNumber(int n, vector<int>& primes) {
        int len = primes.size();
        vector<int> point(len,0);
        vector<int> ugly(n,INT_MAX);
        ugly[0]=1;
        for(int i=1; i<n; ++i){
            for(int j=0; j<len; ++j)
               ugly[i] = min(ugly[i],ugly[point[j]]*primes[j]);
            for(int j=0; j<len; ++j)
                if(ugly[i] == ugly[point[j]]*primes[j]){
                    ++point[j];
                }
        }
        return ugly[n-1];
    }
};