hdu 1042 N!

题目连接

http://acm.hdu.edu.cn/showproblem.php?pid=1042

N!

Description

Given an integer N(0 ≤ N ≤ 10000), your task is to calculate N!

Input

One N in one line, process to the end of file.

Output

For each N, output N! in one line.

Sample Input

1
2
3

Sample Output

1
2
6

用斯特林公式$\begin{align}\large{}n! \approx \large{}\sqrt{2 \pi n}({\frac{n}{e}})^n\end{align}$估计一下阶乘位数，

其余没啥说的，测模板。。

 #include<algorithm>
 #include<iostream>
 #include<istream>
 #include<ostream>
 #include<cstdlib>
 #include<cstring>
 #include<cassert>
 #include<cstdio>
 #include<string>
 using std::max;
 using std::cin;
 using std::cout;
 using std::endl;
 using std::swap;
 using std::string;
 using std::istream;
 using std::ostream;
 struct BigN {
     typedef unsigned long long ull;
     static const int Max_N = ;
     int len, data[Max_N];
     BigN() { memset(data, , sizeof(data)), len = ; }
     BigN(const int num) {
         memset(data, , sizeof(data));
         *this = num;
     }
     BigN(const char *num) {
         memset(data, , sizeof(data));
         *this = num;
     }
     void cls() { len = , memset(data, , sizeof(data)); }
     BigN& clean(){ while (len >  && !data[len - ]) len--;  return *this; }
     string str() const {
         string res = "";
         for (int i = len - ; ~i; i--) res += (char)(data[i] + '');
         if (res == "") res = "";
         res.reserve();
         return res;
     }
     BigN operator = (const int num) {
         int j = , i = num;
         do data[j++] = i % ; while (i /= );
         len = j;
         return *this;
     }
     BigN operator = (const char *num) {
         len = strlen(num);
         for (int i = ; i < len; i++) data[i] = num[len - i - ] - '';
         return *this;
     }
     BigN operator + (const BigN &x) const {
         BigN res;
         int n = max(len, x.len) + ;
         for (int i = , g = ; i < n; i++) {
             int c = data[i] + x.data[i] + g;
             res.data[res.len++] = c % ;
             g = c / ;
         }
         while (!res.data[res.len - ]) res.len--;
         return res;
     }
     BigN operator * (const BigN &x) const {
         BigN res;
         int n = x.len;
         res.len = n + len;
         for (int i = ; i < len; i++) {
             for (int j = , g = ; j < n; j++) {
                 res.data[i + j] += data[i] * x.data[j];
             }
         }
         for (int i = ; i < res.len - ; i++) {
             res.data[i + ] += res.data[i] / ;
             res.data[i] %= ;
         }
         return res.clean();
     }
     BigN operator * (const int num) const {
         BigN res;
         res.len = len + ;
         for (int i = , g = ; i < len; i++) res.data[i] *= num;
         for (int i = ; i < res.len - ; i++) {
             res.data[i + ] += res.data[i] / ;
             res.data[i] %= ;
         }
         return res.clean();
     }
     BigN operator - (const BigN &x) const {
         assert(x <= *this);
         BigN res;
         for (int i = , g = ; i < len; i++) {
             int c = data[i] - g;
             if (i < x.len) c -= x.data[i];
             if (c >= ) g = ;
             else g = , c += ;
             res.data[res.len++] = c;
         }
         return res.clean();
     }
     BigN operator / (const BigN &x) const {
         return *this;
     }
     BigN operator += (const BigN &x) { return *this = *this + x; }
     BigN operator *= (const BigN &x) { return *this = *this * x; }
     BigN operator -= (const BigN &x) { return *this = *this - x; }
     BigN operator /= (const BigN &x) { return *this = *this / x; }
     bool operator <  (const BigN &x) const {
         if (len != x.len) return len < x.len;
         for (int i = len - ; ~i; i--) {
             if (data[i] != x.data[i]) return data[i] < x.data[i];
         }
         return false;
     }
     bool operator >(const BigN &x) const { return x < *this; }
     bool operator<=(const BigN &x) const { return !(x < *this); }
     bool operator>=(const BigN &x) const { return !(*this < x); }
     bool operator!=(const BigN &x) const { return x < *this || *this < x; }
     bool operator==(const BigN &x) const { return !(x < *this) && !(x > *this); }
 };
 istream& operator >> (istream &in, BigN &x) {
     string src;
     in >> src;
     x = src.c_str();
     return in;
 }
 ostream& operator << (ostream &out, const BigN &x) {
     out << x.str();
     return out;
 }
 int main() {
 #ifdef LOCAL
     freopen("in.txt", "r", stdin);
     freopen("out.txt", "w+", stdout);
 #endif
     int n;
     while (~scanf("%d", &n)) {
         BigN res = ;
         if ( == n ||  == n) {
             puts("");
             continue;
         }
         for (int i = ; i <= n; i++) res *= i;
         cout << res << endl;
     }
     return ;
 }