hdu 5363 Key Set

hdu 5363 的传送门

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

题目大意：给你一个数m，然后有m个数，这个数有多少个和是偶数的集合，e:给你3,集合有{1}，{1，2}，{1，3}，
{1，2，3}，{2}，{2，3}，{3}

然而和是偶数的只有{1，2}，{1，3}，{2，3}；

解题思路：推出公式； ans=2 ^ (m-1) - 1;

下面上代码：

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
const int mod = 1000000007;
typedef long long LL;
LL quick(int m)
{
    m-=1;
    LL ans=1;
    LL tmp=2;
    while(m)
    {
        if(m&1)
        {
            ans=ans*tmp%mod;
            m--;
        }
        tmp=(tmp*tmp)%mod;
        m>>=1;
    }
    return ans;
}
int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int m;
        scanf("%d",&m);
        printf("%lld\n",quick(m)-1);
    }
    return 0;
}