Quick power explanation

Fast power

Time complexity O（logn）
(a + b) modp=(a modp + b modp) modp
(a - b) modp = (a modp - b modp + p) modp
a * b modp = a modp * b modp

const long long mod=1e9+7; 
long long fastpow(long long x,long long y){
     
	x%=mod; 
	long long res=1; 
	while(y){
     
		if(y & 1) res=res*x%mod; 
		y>>=1;
		x=x*x%mod; 
	}
	return res; 
}