HDOJ-5363 Key Set

Key Set
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 1688 Accepted Submission(s): 892

Problem Description
soda has a set S with n integers {1,2,…,n}. A set is called key set if the sum of integers in the set is an even number. He wants to know how many nonempty subsets of S are key set.

Input
There are multiple test cases. The first line of input contains an integer T (1≤T≤105), indicating the number of test cases. For each test case:

The first line contains an integer n (1≤n≤109), the number of integers in the set.

Output
For each test case, output the number of key sets modulo 1000000007.

Sample Input
4
1
2
3
4

Sample Output
0
1
3
7

由题意可得出，输出应为2^(n-1)-1。但是数比较大，应该用快速幂。

代码如下：

#include <cstdio>#include <algorithm>#include<stdint.h>#include<math.h>#include<string.h>__int64 quickpow(__int64 n,__int64 m,__int64 mod){    __int64 a=1,b=n;    while(m)    {        if(m&1)        {            a=(b*a)%mod;        }        b=(b*b)%mod;        m>>=1;    }    return a;}using namespace std;int main(){    __int64 t,n,mod=1000000007;    scanf("%I64d",&t);    while(t--)    {        scanf("%I64d",&n);        printf("%I64d\n",quickpow(2,n-1,mod)-1);    }    return 0;}