快速乘模板
logn级别
inline ll mult_mod(ll a, ll b, ll m)
{
ll res = 0;
while(b){
if(b&1) res = (res+a)%m;
a = (a+a)%m;
b >>= 1;
}
return res;
}O(1)级别
inline ll mult_mod(ll a, ll b, ll m)
{
ll c = a*b-(ll)((long double)a*b/m+0.5)*m;
return c<0 ? c+m : c; //就是算的a*b%m;
}
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