Number of Islands (Leetcode 200)

//  Problem: Number of Islands
//  Approach: Depth First Search (DFS)
//  Author: Komal Sikchi
//  Hacktoberfest 2025 Contribution

import java.util.*;

public class Solution {

    // Function to count the number of islands
    public int numIslands(char[][] grid) {
        int row = grid.length;
        int col = grid[0].length;
        int island = 0;

        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (grid[i][j] == '1') {
                    island++;
                    dfs(i, j, grid);
                }
            }
        }
        return island;
    }

    // Depth First Search to mark connected land
    public void dfs(int row, int col, char[][] grid) {
        int newRow = grid.length;
        int newCol = grid[0].length;
        int[][] directions = new int[][]{{0, 1}, {1, 0}, {0, -1}, {-1, 0}};

        if (row < 0 || col < 0 || row >= newRow || col >= newCol || grid[row][col] == '0') return;

        grid[row][col] = '0'; // mark as visited

        for (int[] dir : directions) {
            dfs(row + dir[0], col + dir[1], grid);
        }
    }

    // 🧾 PSAV (Program Save and Verify) Block — contains main() to test the code
    public static void main(String[] args) {
        Solution obj = new Solution();

        // Sample grid (1 = land, 0 = water)
        char[][] grid = {
            {'1', '1', '0', '0', '0'},
            {'1', '1', '0', '0', '0'},
            {'0', '0', '1', '0', '0'},
            {'0', '0', '0', '1', '1'}
        };

        int result = obj.numIslands(grid);
        System.out.println("Number of Islands: " + result);
    }
}