HALLCON - Editorial

editorial
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Problem Link: Connections - Problems - CodeChef

Author: harshit_jain52

If observed carefully, this problem is LCS.

C++ Code 
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'

int solve(vector<int> &nums1, vector<int> &nums2, int n1, int n2)
{
    int dp[n1 + 1][n2 + 1];

    for (int i = 0; i <= n1; i++)
        dp[i][0] = 0;

    for (int j = 0; j <= n2; j++)
        dp[0][j] = 0;

    for (int i = 1; i <= n1; i++)
    {
        for (int j = 1; j <= n2; j++)
        {
            if (nums1[i - 1] == nums2[j - 1])
                dp[i][j] = 1 + dp[i - 1][j - 1];
            else
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1]);
        }
    }

    return dp[n1][n2];
}

int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int x, y;
        cin >> x >> y;
        vector<int> a(x), b(y);

        for (int i = 0; i < x; i++)
        {
            cin >> a[i];
        }

        for (int i = 0; i < y; i++)
        {
            cin >> b[i];
        }

        cout << solve(a, b, x, y) << endl;
    }
}

Time Complexity: O(x*y)