200. Number of Islands | Time: O (n) | Space: O(n)

// Problem: https://leetcode.com/problems/number-of-islands
// Solution: https://www.youtube.com/watch?v=o8S2bO3pmO4


class Solution {
    public int numIslands(char[][] grid) {
        if (grid == null || grid.length == 0) {
            return 0;
        }

        int numOfIslands = 0;

        for(int i = 0; i < grid.length; i++) {
            for(int j = 0; j < grid[i].length; j++) {
                if(grid[i][j] == '1') {
                    numOfIslands += dfs(grid, i, j);
                }
            }
        }

        return numOfIslands;
    }

    public int dfs(char[][] grid, int i, int j) {
        if (i < 0 || i >= grid.length || j < 0 || j >= grid[i].length || grid[i][j] == '0') {
            return 0;
        }

        grid[i][j] = '0';

        dfs(grid, i + 1, j);
        dfs(grid, i - 1, j);
        dfs(grid, i, j + 1);
        dfs(grid, i, j - 1);

        return 1;
    }
}