NYOJ420 p次方求和 快速幂取模

原题链接

复杂度O(logn);

#include <cstdio>
#define mod 10003

int f(int a, int n){
	if(n == 0) return 1 % mod;
	if(n == 1) return a % mod;
	int t = f(a, n / 2);
	t = t * t % mod;
	if(n & 1) return t * a % mod;
	return t;
}

int main(){
	int t, a, n, s, i;
	scanf("%d", &t);
	while(t-- && scanf("%d%d", &n, &a)){
		for(i = 1, s = 0; i <= n; ++i)
			s += f(i, a), s %= mod;
		printf("%d\n", s);
	}
	return 0;
}

原文：http://blog.csdn.net/chang_mu/article/details/19576431