implement a two dimensional array filled with zeroes and ones. Ones in the two dimensional array makes islands. Find the largest island in the two dimensional array

class Solution {
  public int largestIsland(int[][] grid) {
    // create a map to store the index and area
    Map<Integer, Integer> map = new HashMap<>();
    int index = 2;
    int max = 0;
    for (int i = 0; i < grid.length; i++) {
      for (int j = 0; j < grid[0].length; j++) {
        if (grid[i][j] == 1) {
          int area = dfs(grid, i, j, index);
          map.put(index, area);
          max = Math.max(max, area);
          index++;
        }
      }
    }
    // if all ones, return the area
    if (index == 2) return grid.length * grid[0].length;
    // loop through each zero element and find largest area by merging islands
    for (int i = 0; i < grid.length; i++) {
      for (int j = 0; j < grid[0].length; j++) {
        if (