1.java

class Solution {
    public int maxAreaOfIsland(int[][] grid) {
        int res = 0;
        for (int r = 0; r < grid.length; r++) {
            for (int c = 0; c < grid[0].length; c++) {
                if (grid[r][c] == 1) {
                    int a = area(grid, r, c);
                    res = Math.max(res, a);
                }
            }
        }
        return res;
    }

    int area(int[][] grid, int r, int c) {
        if (!inArea(grid, r, c)) {
            return 0;
        }
        if (grid[r][c] != 1) {
            return 0;
        }
        grid[r][c] = 2;

        return 1
            + area(grid, r - 1, c)
            + area(grid, r + 1, c)
            + area(grid, r, c - 1)
            + area(grid, r, c + 1);
    }

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