Problem: Number of Islands

Question

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Answer: 1

Example 2:

Answer: 3

Solution

TODO

Code

class Solution {
    public int numIslands(char[][] grid) {
        int lands = 0;
        if(grid.length == 0 || grid[0].length == 0) return lands;
        
        int width = grid.length;
        int height = grid[0].length;
        
        for(int i=0; i<width; i++) {
            for(int j=0; j<height; j++) {
                if(grid[i][j] == '1') {
                    traverse(i, j, grid);
                    lands ++;
                }
            }   
        }
        
        return lands;
    }
    
    public void traverse(int i, int j, char[][] grid) {
        int width = grid.length;
        int height = grid[0].length;
        if(grid[i][j] == '1') {
            // set to 0. so it is visited...
            grid[i][j] = '0';
            if(i > 0) traverse(i-1, j, grid);
            if(i < width-1) traverse(i+1,j, grid);
            if(j > 0) traverse(i, j-1, grid);
            if(j < height-1) traverse(i,j+1, grid);
        }
    }
}

Performance