Here is my code for the problem at https://www.codechef.com/ZCOPRAC/problems/ZCO16002 :

```
#include <bits/stdc++.h>
using namespace std;
int dp[2507][2507], n, h[2507], location[100007];
int main()
{
memset(dp, -1, sizeof(dp));
memset(location, -1, sizeof(location));
cin >> n;
for(int i=0; i<n; i++)
cin >> h[i];
sort(h,h+n);
for(int i=0; i<n; i++)
location[h[i]] = i;
int max_len = 0;
for(int i=1; i<n; i++)
dp[0][i] = 2;
for(int i=1; i<n; i++)
dp[i][0] = 2;
for(int i=0; i<n; i++)
dp[i][i] = 1;
for(int i=0; i<n; i++)
{
for(int j=0; j<n; j++)
{
if(i == j || dp[i][j] > 0)
continue;
else
{
int diff = h[j] - h[i];
int prev = h[i] - diff;
if(prev >= 0)
{
int index = location[prev];
if(index != -1)
{
if(dp[index][j] == -1)
dp[i][j] = 2;
else
dp[i][j] = dp[index][i] + 1;
}
else
dp[i][j] = 2;
}
else
dp[i][j] = 2;
}
max_len = max(max_len, dp[i][j]);
}
}
cout << max_len << "\n";
return 0;
}
```

The above code gives the correct output for the sample test case but it gives Runtime Error on submission. Also I am not sure if the above code is actually correct or it fails on some test case. Actually the editorial for this problem ZCO16002 - Editorial contains a recursive solution but since I am still not that good at recursion I tried an iterative approach but here I am stuck with a Runtime Error. Can anyone please help?