【算法】快速幂

a^23 = a^16 * a^4 * a^2 * a^1

res=a^1

res*=a^2

res*=a^4

res*=a^16

...

#include<bits/stdc++.h>
#define ll long long
using namespace std;
int main(){
    ll a,b,p,res=1;
    cin>>a>>b>>p;
    while(b){
        if(b&1)res=res*a%p;//当前位是1
        a=a*a%p;//使得a顺次变成a^1 a^2 a^4 a^8 ...
        b/=2;
	}
    cout<<res<<endl;
    return 0;
}