快速幂取模

 1 typedef long long ll; 
 2 ll mod_pow(ll x, ll n, ll mod){
 3     ll res = 1;
 4     while( n > 0 ){ 
 5         if( n & 1 ) res = res * x % mod;
 6         x = x * x % mod;
 7         n >>= 1; 
 8     }
 9     return res;
10 }

 递归版

1 typedef long long ll;
2 ll mod_pow(ll x, ll n, ll mod){
3     if( n == 0 ) return 1;
4     ll res = mod_pow( x * x % mod, n / 2, mod );
5     if( n & 1 ) res = res * x % mod;
6     return res;
7 }