Hello guys. I was solving CSES - Coin Combinations II problem and end up with a solution as followed, but for a reason, I got time limit on several test cases.

Here is my solution:

```
#include <bits/stdc++.h>
using namespace std;
using lli = int64_t;
using pii = pair < int, int > ;
using vint = vector < int > ;
using triple = pair < int, pii > ;
const int MX = 1e6 + 5;
const int MXC = 105;
const int MOD = 1e9 + 7;
int n;
int coins[MXC];
int dp[MX][MXC];
int solution(int x, int k) {
if (x < 0 || k < 0) return 0;
if (x == 0) return dp[x][k] = 1;
if (dp[x][k] != -1) return dp[x][k];
return dp[x][k] = (solution(x - coins[k], k) + solution(x, k - 1)) % MOD;
}
void solve() {
int x;
cin >> n >> x;
for (int i = 0; i < n; i++) cin >> coins[i];
sort(coins, coins + n);
for (int i = 0; i <= x; i++) {
fill(dp[i], dp[i] + n, -1);
}
cout << solution(x, n - 1);
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int t = 1;
// cin >> t;
while (t--) {
solve();
cout << '\n';
}
return 0;
}
```

But I don’t get it why? My solution’s time complexity must be O(nx), and nx must be ok for this problem, but why do I get a time limit? What’s wrong with this code? I want to learn and prevent this type of error again.