1using System;
2using System.Collections.Generic;
3
4public class Solution {
5    public int[][] FindFarmland(int[][] land) {
6        int m = land.Length;
7        int n = land[0].Length;
8        bool[,] visited = new bool[m, n];
9        var results = new List<int[]>();
10
11        for (int i = 0; i < m; i++) {
12            for (int j = 0; j < n; j++) {
13                if (land[i][j] == 1 && !visited[i, j]) {
14                    int maxRow = i, maxCol = j;
15                    var queue = new Queue<(int, int)>();
16                    queue.Enqueue((i, j));
17                    visited[i, j] = true;
18
19                    while (queue.Count > 0) {
20                        var (row, col) = queue.Dequeue();
21                        maxRow = Math.Max(maxRow, row);
22                        maxCol = Math.Max(maxCol, col);
23
24                        int[,] directions = { {0, 1}, {1, 0} };
25                        for (int d = 0; d < directions.GetLength(0); d++) {
26                            int newRow = row + directions[d, 0], newCol = col + directions[d, 1];
27                            if (newRow < m && newCol < n && land[newRow][newCol] == 1 && !visited[newRow, newCol]) {
28                                visited[newRow, newCol] = true;
29                                queue.Enqueue((newRow, newCol));
30                            }
31                        }
32                    }
33                    results.Add(new int[] { i, j, maxRow, maxCol });
34                }
35            }
36        }
37        return results.ToArray();
38    }
39}

using System.Collections.Generic;

public class Solution {
    public int[][] FindFarmland(int[][] land) {
        int m = land.Length, n = land[0].Length;
        int[] parent = new int[m * n];
        int[] rank = new int[m * n];

        for (int i = 0; i < m * n; i++) {
            parent[i] = i;
        }

        int Find(int x) {
            if (parent[x] != x) {
                parent[x] = Find(parent[x]);
            }
            return parent[x];
        }

        void Union(int x, int y) {
            int rootX = Find(x);
            int rootY = Find(y);
            if (rootX != rootY) {
                if (rank[rootX] > rank[rootY]) {
                    parent[rootY] = rootX;
                } else if (rank[rootX] < rank[rootY]) {
                    parent[rootX] = rootY;
                } else {
                    parent[rootY] = rootX;
                    rank[rootX]++;
                }
            }
        }

        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (land[i][j] == 1) {
                    int index = i * n + j;
                    if (i > 0 && land[i-1][j] == 1) {
                        Union(index, (i-1) * n + j);
                    }
                    if (j > 0 && land[i][j-1] == 1) {
                        Union(index, i * n + (j-1));
                    }
                }
            }
        }

        var bounds = new Dictionary<int, int[]>();
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (land[i][j] == 1) {
                    int root = Find(i * n + j);
                    if (!bounds.ContainsKey(root)) {
                        bounds[root] = new int[] { i, j, i, j };
                    } else {
                        bounds[root][0] = Math.Min(bounds[root][0], i);
                        bounds[root][1] = Math.Min(bounds[root][1], j);
                        bounds[root][2] = Math.Max(bounds[root][2], i);
                        bounds[root][3] = Math.Max(bounds[root][3], j);
                    }
                }
            }
        }

        var result = new List<int[]>(bounds.Values); 
        return result.ToArray();
    }
}