【题解】洛谷 P1134 [USACO3.2]阶乘问题

 1 #include <iostream>
 2 using namespace std;
 3 
 4 int main() {
 5     int n;
 6     cin >> n;
 7     int c = 1, a = 0, b = 0;
 8     for(int i = 1; i <= n; i++) {
 9         int x = i;
10         while(x % 2 == 0) x /= 2, a++;
11         while(x % 5 == 0) x /= 5, b++;
12         c = (c * x) % 10;
13     }
14     for(int i = 0; i < a - b; i++) {
15         c = (c * 2) % 10;
16     }
17     cout << c << endl;
18     return 0;
19 }