2319. Check if Matrix Is X-Matrix

A square matrix is said to be an X-Matrix if both of the following conditions hold:

1. All the elements in the diagonals of the matrix are non-zero.
2. All other elements are 0.

Given a 2D integer array grid of size n x n representing a square matrix, return true if grid is an X-Matrix. Otherwise, return false.

class Solution {
public:
    bool checkXMatrix(vector<vector<int>>& grid) {
        int n = grid.size(), m = grid[0].size();
        for(int i = 0, l = 0, r = m - 1; i < n; i++,l++,r--) {
            if(grid[i][l] == 0) return false;
            if(grid[i][r] == 0) return false;
            grid[i][l] = grid[i][r] = -1;
        }
        for(int i = 0; i < n; i++) {
            for(int j = 0; j < m; j++) {
                if(grid[i][j] == -1) continue;
                if(grid[i][j]) return false;
            }
        }
        return true;
    }
};