If there exists a sub-array with sum K

Question

Given an array of positive integers, which is the most efficient way to find if there exists a sub-array (not necessarily continuous) such that the sum of its elements is equal to a given number k.
My approach was a naive recursive one:

#include <iostream>
#include <algorithm>
#include <utility>
#include <stdio.h>
#include <queue>
#include <climits>
#include <malloc.h>
#include <stdlib.h>
#include <cstring>
#include <cmath>
#include <sstream>
#include <map>
#include <stack>
#include <string>
#include <ctime>
using namespace std;
int flag=0;
void solve(int ind,int n,int arr[],int sum,int k)
{
    if(sum>k)
        return;
    if(sum==k){
        flag++;
        return;
    }
    for(int i=ind+1;i<n;i++)
        solve(i,n,arr,sum+arr[i],k);
}
int main()
{
    int t;
    cin >> t;//number of test cases
    while(t--)
    {
        int n,k;//n->number of array elements
        cin >> n >> k;//k->given number
        int arr[n];
        for(int i=0;i<n;i++)
            cin >> arr[i];
        for(int i=0;i<n;i++)
            solve(i,n,arr,arr[i],k);
        if(flag>0)
            cout << "YES!" << endl;
        else
            cout << "NO!" << endl;
        flag=0;
    }
    return 0;
}