题解 P2415 【集合求和】

mrwalking · 2018-01-29 18:18:18 · 题解

//P2415 集合求和
//研究 1 2 3 4
//子集[] [1] [2] [3] [4] [1 2] [1 3] [1 4] [2 3] [2 4] [3 4] [1 2 3] [1 2 4] [1 3 4] [2 3 4] [1 2 3 4]
//1*8+2*8+3*8+4*8=(1+2+3+4)*2^(4-1) 
//发现规律 输入元素和*2^(n-1) 
#include <stdio.h>
int main(){
    long long ans=0;
    int n=0,i,a;
    while(scanf("%d",&a)!=EOF)ans+=a,n++;
    for(i=1;i<n;i++)ans*=2;
    printf("%lld",ans);
    return 0;
}