深搜之搜索树

#include <cstdio>
int a[30];int n,k;
bool dfs(int i,int sum)  //前i项之和sum
{
    if(i==n)
        return sum==k;
    if(dfs(i+1,sum))  //放入第i个
        return true;
    if(dfs(i+1,sum+a[i]))  //不放入第i个
        return true;
}
int main()
{
    while(~scanf("%d%d",&n,&k))
    {
        for(int i=0;i<n;i++)
            scanf("%d",&a[i]);
        if(dfs(0,0))
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}

#include <iostream>
#include <vector>
using namespace std;
int a[4]={1,2,4,7},k;
vector<int> ans;
void dfs(int i,int sum)
{
	if(i==4){
		if(sum==k)
	   	{
   			for(int i=0;i!=ans.size();i++)cout<<ans[i]<<" ";
			cout<<endl;
			return ;
   		}
   		else 
		 return ;
	}
	dfs(i+1,sum);
	ans.push_back(a[i]);
	dfs(i+1,sum+a[i]);
	ans.pop_back();
	return ;
}
int main()
{
	 k=7;
	 dfs(0,0);
}