Number of Islands

gistfile1.txt

/**
 * @param {character[][]} grid
 * @return {number}
 */
var numIslands = function(grid) {
    var visited = grid.map(array => array.map(e => false));
    var counter = 0;
    
    var visit = function(i, j) {
        visited[i][j] = true;
        
        if (i > 0 && grid[i - 1][j] === '1' && !visited[i - 1][j]) {
            visit(i - 1, j);
        }
        
        if (i < grid.length - 1 && grid[i + 1][j] === '1' && !visited[i + 1][j]) {
            visit(i + 1, j);
        }
        
        if (j > 0 && grid[i][j - 1] && grid[i][j - 1] === '1' && !visited[i][j - 1]) {
            visit(i, j - 1);
        }
        
        if (j < grid[i].length - 1 && grid[i][j + 1] === '1' && !visited[i][j + 1]) {
            visit(i, j + 1);
        }
    }
    
    for (var i = 0; i < grid.length; i++) {
        for (var j = 0; j < grid[i].length; j++) {
            if (grid[i][j] === '1' && !visited[i][j]) {
                visit(i, j);
                counter++;
            }
        }
    }

    return counter;
};