[LeetCode]313 超级丑数

Super Ugly Number(超级丑数)

【难度：Medium】

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 ≤ 10^6, 0 < primes[i] < 1000.

超级丑数是指一个所有素数因子只在给定的k个素数表中的正整数，1是特殊的超级丑数。给定k大小的素数表，求出第n个超级丑数。

解题思路

下一个丑数建立在当前的丑数分别乘以素数表的素数所得到的最小值来构成，因此通过代码模拟这一过程即可。

c++代码如下：

class Solution {
public:
int nthSuperUglyNumber(int n, vector<int>& primes) {
if (n == 1)
return 1;
int l = primes.size();
vector<int> ugly(n,INT_MAX);
vector<int> tmp(l,1);
vector<int> count(l,0);
int next = 1;
for (int i = 0; i < n; i++) {
ugly[i] = next;
next = INT_MAX;
for (int j = 0; j < l; j++) {
//cout << "j "  << j << " tmp " << tmp[j] << " ugly " << ugly[i] << " count " << count[j] << " next " << next << endl;
if (tmp[j] == ugly[i]) {
tmp[j] = ugly[count[j]]*primes[j];
count[j]++;
}
next = min(next,tmp[j]);

}

}
return ugly[n-1];
}
};