N的阶乘的长度。
那不就是 (int)log10(N!) 吗~~~
(int)log10(99) = 1 ,(int)log10(100) = 2.
#include <cstdio> #include <algorithm> #include <iostream> #include <cmath> #define LL long long using namespace std; int main() { LL a; cin>>a; double sum = 1; for(LL i = 1;i <= a;i ++) sum += log10(i); cout<<(int)sum<<endl; return 0; }