Google Coding Interviews Number of Islands (LeetCode) and explanation. One of Google's most commonly asked interview questions according to LeetCode. This coding interview question is commonly asked by companies like: Google, Facebook, Snapchat, Amazon, Uber, LinkedIn, Microsoft, Apple and many others.

numberOfIslands.js

/**
 * @param {character[][]} grid
 * @return {number}
 */

var dfs = function(grid, i, j) {
    
    const w = grid.length;
    const h = grid[0].length;
    
    if ( i >= 0 && i < w && j >= 0 && j < h && grid[i][j] == '1') {
        grid[i][j] = '0'
        
        dfs(grid, i+1, j); //right
        dfs(grid, i-1, j); //left
        dfs(grid, i, j+1); //below
        dfs(grid, i, j-1); //above
    }
}


var numIslands = function(grid) {
    let islands = 0;
    
    if(grid.length == 0) {
        return 0;
    }
    
    const w = grid.length;
    const h = grid[0].length;
    
    for (let i=0; i<w; i++) {
        for(let j=0; j<h; j++) {
            const char = grid[i][j];
            
            if (char == '1') {
                dfs(grid, i, j);
                islands += 1;
            }
        }
    }
    
    return islands;
};