Flip Square Submatrix Vertically

/**
 * @param {number[][]} grid
 * @param {number} x
 * @param {number} y
 * @param {number} k
 * @return {number[][]}
 */
var reverseSubmatrix = function(grid, x, y, k) {
    const rows = k / 2;

    for (let row = 0; row < rows; row++) {
        for (let col = 0; col < k; col++) {
            const inv_row = k - 1 - row;

            if (row !== inv_row) {
                const temp = grid[x + row][y + col];
                grid[x + row][y + col] = grid[x + inv_row][y + col];
                grid[x + inv_row][y + col] = temp;
            }
        }
    }

    return grid;
};