695_Max_Area_of_Island.java

/*class Solution {
    int[][] grid;

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

    public int maxAreaOfIsland(int[][] grid) {
        this.grid = grid;
        int ans = 0;
        for (int r = 0; r < grid.length; r++) {
            for (int c = 0; c < grid[0].length; c++) {
                ans = Math.max(ans, area(r, c));
            }
        }
        return ans;
    }
}*/
class Solution {
    // DFS and you can implement BFS with queue
    public int maxAreaOfIsland(int[][] grid) {
        int[] dr = new int[]{1, -1, 0, 0};
        int[] dc = new int[]{0, 0, 1, -1};
        int ans = 0;
        for (int r0 = 0; r0 < grid.length; r0++) {
            for (int c0 = 0; c0 < grid[0].length; c0++) {
                if (grid[r0][c0] == 1) {
                    int shape = 0;
                    Stack<int[]> stack = new Stack();
                    stack.push(new int[]{r0, c0});
                    grid[r0][c0] = 0;
                    while (!stack.empty()) {
                        int[] node = stack.pop();
                        int r = node[0], c = node[1];
                        shape++;
                        for (int k = 0; k < 4; k++) {
                            int nr = r + dr[k];
                            int nc = c + dc[k];
                            if (0 <= nr && nr < grid.length &&
                                    0 <= nc && nc < grid[0].length &&
                                    grid[nr][nc] == 1) {
                                stack.push(new int[]{nr, nc});
                                grid[nr][nc] = 0;
                            }
                        }
                    }
                    ans = Math.max(ans, shape);
                }
            }
        }
        return ans;
    }
}