hd 5363 Key Set（快速幂）

Key Set

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 131072/131072 K (Java/Others)
Total Submission(s): 1811    Accepted Submission(s): 952

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

41234

 

Sample Output

0137
题意 ：求真子集  即 s=2^(n-1)-1
#include<stdio.h>__int64 quickpow(__int64 a,__int64 b){__int64 ans = 1,base = a % 1000000007;while(b){if(b & 1){ans=(base * ans) % 1000000007;}base = (base * base) % 1000000007;b >>= 1;}return ans;}int main(){int t,n;scanf("%d",&t);while(t--){    scanf("%d",&n);    printf("%I64d\n",quickpow(2,n-1)-1);}return 0;}