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  • HDU5363:Key Set

    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 (1T105), indicating the number of test cases. For each test case:

    The first line contains an integer n (1n109), 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
     

    Source


    看数字找规律吧。。。

    随便试试竟然就试过了。


    #include <iostream>
    #include <stdio.h>
    #include <string.h>
    #include <stack>
    #include <queue>
    #include <map>
    #include <set>
    #include <vector>
    #include <math.h>
    #include <bitset>
    #include <algorithm>
    #include <climits>
    using namespace std;
    
    #define ls 2*i
    #define rs 2*i+1
    #define UP(i,x,y) for(i=x;i<=y;i++)
    #define DOWN(i,x,y) for(i=x;i>=y;i--)
    #define MEM(a,x) memset(a,x,sizeof(a))
    #define W(a) while(a)
    #define gcd(a,b) __gcd(a,b)
    #define LL long long
    #define N 1005
    #define INF 0x3f3f3f3f
    #define EXP 1e-8
    #define rank rank1
    const int mod = 1000000007;
    LL ppow(LL a,LL b)
    {
        LL c=1;
        while(b)
        {
            if(b&1) c=c*a%mod;
            b>>=1;
            a=a*a%mod;
        }
        return c;
    }
    int main()
    {
        int t;
        LL n;
        scanf("%d",&t);
        while(t--)
        {
            scanf("%I64d",&n);
            printf("%I64d
    ",ppow(2,n-1)-1);
        }
    
        return 0;
    }


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  • 原文地址:https://www.cnblogs.com/tlnshuju/p/7158423.html
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