N的阶乘的长度 斯特林近似

51Nod1130https://vjudge.net/problem/51Nod-1130

long long res = (long long)((log10(sqrt(4.0 * acos(0.0) * n)) + n * (log10(n) - log10(exp(1.0)))) + 1);

#include<bits/stdc++.h>const int INF  = 0x3f3f3f3f;const int Maxn = 500005;#define ll long long#define mem(x,y) memset(x,y,sizeof(x))using namespace std;int main() {    int T, n;    cin >> T;    while (T--) {        cin >> n;        long  long res = (long long)((log10(sqrt(4.0 * acos(0.0) * n)) + n * (log10(n) - log10(exp(1.0)))) + 1);        if (n == 1) res = 1;        cout << res << endl;    }}