# 快速幂-HDOJ-5363-Key Set

Key Set

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 1175 Accepted Submission(s): 669

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

``//// main.cpp// 150806-1011//// Created by 袁子涵 on 15/8/6.// Copyright (c) 2015年 袁子涵. All rights reserved.//#include <iostream>#include <string.h>#include <stdio.h>#include <stdlib.h>using namespace std;unsigned long long int T;unsigned long long int n;unsigned long long int a,b,c;long long result(long long a,long long b,long long m){ long long d,t; d=1; t=a; while (b>0) { if (b%2==1) d=(d*t)%m; b/=2; t=(t*t)%m; } return d;}int main(int argc, const char * argv[]) { cin >> T; while (T--) { scanf("%llu",&n); if (n==1) { printf("0/n"); continue; } b=result(2, n-1, 1000000007); cout << (b-1) << endl; } return 0;}``