HDU 4704 SUM(费马小定理)

// File Name: 4704.c
// Author: darkdream
// Created Time: 2013年09月08日 星期日 20时32分42秒

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<time.h>
#include<math.h>
#define LL long long
#define maxn 100009
#define mod 1000000007
//freopen("/home/plac/problem/input.txt","r",stdin);
//freopen("/home/plac/problem/output.txt","w",stdout);

char str[maxn];
LL a[maxn];
LL POW (LL n ,LL k )
{
LL ans = 1;
LL p = n;
while(k)
{
if(k &1)
ans =(ans * p)%mod ;
p = p*p %mod;
k >>=1;
}
return ans;
}
LL len ;
LL chu(LL k){
LL temp = 0;
for(int i = len;i >=1 ;i --)
{
temp = temp*10 + a[i];
if(temp > k )
temp = temp%k;
}
return temp;
}
void jian()
{
for(int i = 1;i <= len ;i ++)
{
if(a[i] >= 1)
{
a[i] -= 1;
return;
}
else
a[i] = 9;
}
}
int main(){
while(scanf("%s",&str[1]) != EOF)
{
len = strlen(&str[1]);
for(int i = 1; i<= len ;i ++)
a[i] = str[len-i+1] - '0';
jian();
LL k = chu(mod-1);
printf("%lld\n",POW(2,k));
}

return 0 ;
}