Count Islands With Total Value Divisible by K

/**
 * @param {number[][]} grid
 * @param {number} k
 * @return {number}
 */
var countIslands = function(grid, k) {
    const rows = grid.length;
    const cols = grid[0].length;
    let res = 0;

    const explore = (row, col) => {
        if (row < 0 || row >= rows || col < 0 || col >= cols || grid[row][col] === 0) {
            return 0;
        }

        const val = grid[row][col];

        grid[row][col] = 0;

        return val +
            explore(row, col + 1) +
            explore(row + 1, col) +
            explore(row, col - 1) +
            explore(row - 1, col);
    };

    for (let row = 0; row < rows; row++) {
        for (let col = 0; col < cols; col++) {
            if (grid[row][col] !== 0) {
                const sum = explore(row, col);
                if (sum % k === 0) {
                    res++;
                }
            }
        }
    }

    return res;
};