MaxAreaOfIsland.java

class Solution {

    private static final int[][] DIRS = new int[][] {
        new int[] {-1,0},
        new int[] {1,0},
        new int[] {0,-1},
        new int[] {0,1}
    };

    public int maxAreaOfIsland(int[][] grid) {
        int ans = 0;
        for (int r = 0; r < grid.length; r++) {
            for (int c = 0; c < grid[r].length; c++) {
                if (grid[r][c] == 1) {
                    int area = sumArea(grid, r, c);
                    if (area > ans) {
                        ans = area;
                    }
                }
            }
        }
        return ans; 
    }

    private int sumArea(int[][] grid, int r, int c) {
        if (!isInbound(grid, r, c) || grid[r][c] == 0) {
            return 0;
        }
        int area = 1;
        grid[r][c] = 0;
        for (var dir : DIRS) {
            area += sumArea(grid, r + dir[0], c + dir[1]);
        }
        return area;
    }

    private boolean isInbound(int[][] grid, int r, int c) {
        return r >= 0 && r < grid.length && c >= 0 && c < grid[r].length;
    }
}