时间复杂度O(logn)
public static int getPower(int k, int N) {
if(N==0)
return 1;
long temp = k;
long res = 1;
for(int i=N;i>0;){
if((i&1)!=0){
res *=temp;
}
temp =(temp * temp)%1000000007;
res = res %1000000007;
i = i>> 1;
}
return (int)res;
}