Problem Description
soda has a set S are key set.
Input
There are multiple test cases. The first line of input contains an integer ),
indicating the number of test cases. For each test case:
The first line contains an integer ), the number of integers in the set.
The first line contains an integer ), 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
给你一个1-n的集合，问你有多少个子集的元素和为偶数
假设偶数有a个，奇数有b个,总数为n：
偶：C（0, a）+ C（1 , a）....... + C（a, a） = 2 ^ a
奇：C（0, b）+ C（2 , b）....... + C（b, b） = 2 ^ (b - 1)
all = 偶 * 奇 - 1（奇偶中都不选的情况）；
---> all = 2 ^ (a + b - 1)- 1 = 2 ^ (n - 1) -1
#include <iostream>
#include <cstdio>
#include <vector>
#pragma comment(linker, "/STACK:102400000,102400000")
using namespace std;
typedef long long ll;
char ma[1100][1100];
int ln, lm;
const int mod = 1000000007;
ll pow_mod(int a,int n)
{
if(n == 0)
return 1;
ll x = pow_mod(a,n/2);
ll ans = (ll)x*x%mod;
if(n %2 == 1)
ans = ans *a % mod;
return ans;
}
int main()
{
int T;
scanf("%d",&T);
while(T--)
{
int n;
scanf("%d",&n);
ll sum1 = (pow_mod(2,n-1)-1)%mod;
printf("%I64d\n",sum1);
}
return 0;
}