The partial sum problem

The partial sum problem

时间限制：1000 ms | 内存限制：65535 KB
难度：2

描述One day,Tom’s girlfriend give him an array A which contains N integers and asked him:Can you choose some integers from the N integers and the sum of them is equal to K.

输入There are multiple test cases.

Each test case contains three lines.The first line is an integer N(1≤N≤20),represents the array contains N integers. The second line contains N integers,the ith integer represents A[i](-10^8≤A[i]≤10^8).The third line contains an integer K(-10^8≤K≤10^8).
输出If Tom can choose some integers from the array and their them is K,printf ”Of course,I can!”; other printf ”Sorry,I can’t!”.
样例输入

4
1 2 4 7
13
4
1 2 4 7
15

样例输出

Of course,I can!
Sorry,I can't!

部分和问题！

#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
long long a[25],n,sum,sum1;
int visited[25];
bool success;
void dfs(int k)
{
    int i;
    if(success==true)
    {
        return;
    }
    if(sum1>=sum)
    {
        if(sum1==sum)
        {
            success=true;
            cout<<"Of course,I can!"<<endl;
        }
        return;
    }
    for(i=k;i<=n;i++)
    {
        sum1+=a[i];
        visited[i]=1;
        dfs(i+1);
        sum1-=a[i];
        visited[i]=0;
    }
}
int main()
{
    int i;
    while(cin>>n)
    {
        success=false;
        sum1=0;
        memset(a,0,sizeof(a));
        memset(visited,0,sizeof(visited));
        for(i=1;i<=n;i++)
        {
            cin>>a[i];
        }
        cin>>sum;
        dfs(1);
        if(!success)
        {
            cout<<"Sorry,I can't!"<<endl;
        }
    }
}