2373. Largest Local Values in a Matrix

You are given an n x n integer matrix grid.

Generate an integer matrix maxLocal of size (n - 2) x (n - 2) such that:

• maxLocal[i][j] is equal to the largest value of the 3 x 3 matrix in grid centered around row i + 1 and column j + 1.

In other words, we want to find the largest value in every contiguous 3 x 3 matrix in grid.

Return the generated matrix.

class Solution {
public:
    vector<vector<int>> largestLocal(vector<vector<int>>& grid) {
        int n = grid.size(), m = grid[0].size();
        vector<vector<int>> res(n-2, vector<int>(m-2, INT_MIN));
        for(int i = 0; i < n - 2; i++) {
            for(int j = 0; j < m - 2; j++) {
                for(int k = 0; k < 3; k++) {
                    for(int l = 0; l < 3; l++) {
                        res[i][j] = max(res[i][j], grid[i+k][j+l]);
                    }
                }
            }
        }
        return res;
    }
};