Added task 1992.

Author: javadev

src/main/java/g1901_2000/s1992_find_all_groups_of_farmland/Solution.java

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+package g1901_2000.s1992_find_all_groups_of_farmland;
+
+// #Medium #Array #Depth_First_Search #Breadth_First_Search #Matrix
+// #2022_05_19_Time_7_ms_(89.08%)_Space_52.1_MB_(87.32%)
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Solution {
+ private final List<int[]> res = new ArrayList<>();
+
+ public int[][] findFarmland(int[][] land) {
+ if (land == null || land.length == 0) {
+ return new int[][] {};
+ }
+ int m = land.length;
+ int n = land[0].length;
+ for (int i = 0; i < m; i++) {
+ for (int j = 0; j < n; j++) {
+ if (land[i][j] == 1) {
+ int[] dirs = new int[4];
+ dirs[0] = i;
+ dirs[1] = j;
+ dirs[2] = i;
+ dirs[3] = j;
+ dfs(land, i, j, dirs);
+ res.add(dirs);
+ }
+ }
+ }
+ return res.toArray(new int[0][]);
+ }
+
+ private void dfs(int[][] land, int i, int j, int[] dirs) {
+ if (i < 0 || i >= land.length || j < 0 || j >= land[0].length || land[i][j] != 1) {
+ return;
+ }
+ land[i][j] = -1;
+ dfs(land, i + 1, j, dirs);
+ dfs(land, i, j + 1, dirs);
+ dirs[0] = Math.min(dirs[0], i);
+ dirs[1] = Math.min(dirs[1], j);
+ dirs[2] = Math.max(dirs[2], i);
+ dirs[3] = Math.max(dirs[3], j);
+ }
+}

src/main/java/g1901_2000/s1992_find_all_groups_of_farmland/readme.md

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+1992\. Find All Groups of Farmland
+
+Medium
+
+You are given a **0-indexed** `m x n` binary matrix `land` where a `0` represents a hectare of forested land and a `1` represents a hectare of farmland.
+
+To keep the land organized, there are designated rectangular areas of hectares that consist **entirely** of farmland. These rectangular areas are called **groups**. No two groups are adjacent, meaning farmland in one group is **not** four-directionally adjacent to another farmland in a different group.
+
+`land` can be represented by a coordinate system where the top left corner of `land` is `(0, 0)` and the bottom right corner of `land` is `(m-1, n-1)`. Find the coordinates of the top left and bottom right corner of each **group** of farmland. A **group** of farmland with a top left corner at <code>(r<sub>1</sub>, c<sub>1</sub>)</code> and a bottom right corner at <code>(r<sub>2</sub>, c<sub>2</sub>)</code> is represented by the 4-length array <code>[r<sub>1</sub>, c<sub>1</sub>, r<sub>2</sub>, c<sub>2</sub>].</code>
+
+Return _a 2D array containing the 4-length arrays described above for each **group** of farmland in_ `land`_. If there are no groups of farmland, return an empty array. You may return the answer in **any order**_.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-23-15-copy-of-diagram-drawio-diagrams-net.png)
+
+**Input:** land = [[1,0,0],[0,1,1],[0,1,1]]
+
+**Output:** [[0,0,0,0],[1,1,2,2]]
+
+**Explanation:**
+
+The first group has a top left corner at land[0][0] and a bottom right corner at land[0][0].
+
+The second group has a top left corner at land[1][1] and a bottom right corner at land[2][2]. 
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-30-26-copy-of-diagram-drawio-diagrams-net.png)
+
+**Input:** land = [[1,1],[1,1]]
+
+**Output:** [[0,0,1,1]]
+
+**Explanation:**
+
+The first group has a top left corner at land[0][0] and a bottom right corner at land[1][1]. 
+
+**Example 3:**
+
+![](https://assets.leetcode.com/uploads/2021/07/27/screenshot-2021-07-27-at-12-32-24-copy-of-diagram-drawio-diagrams-net.png)
+
+**Input:** land = [[0]]
+
+**Output:** []
+
+**Explanation:** There are no groups of farmland. 
+
+**Constraints:**
+
+* `m == land.length`
+* `n == land[i].length`
+* `1 <= m, n <= 300`
+* `land` consists of only `0`'s and `1`'s.
+* Groups of farmland are **rectangular** in shape.

src/test/java/g1901_2000/s1992_find_all_groups_of_farmland/SolutionTest.java

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+package g1901_2000.s1992_find_all_groups_of_farmland;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+ @Test
+ void findFarmland() {
+ assertThat(
+ new Solution().findFarmland(new int[][] {{1, 0, 0}, {0, 1, 1}, {0, 1, 1}}),
+ equalTo(new int[][] {{0, 0, 0, 0}, {1, 1, 2, 2}}));
+ }
+
+ @Test
+ void findFarmland2() {
+ assertThat(
+ new Solution().findFarmland(new int[][] {{1, 1}, {1, 1}}),
+ equalTo(new int[][] {{0, 0, 1, 1}}));
+ }
+
+ @Test
+ void findFarmland3() {
+ assertThat(new Solution().findFarmland(new int[][] {{0}}), equalTo(new int[][] {}));
+ }
+
+ @Test
+ void findFarmland4() {
+ assertThat(new Solution().findFarmland(new int[][] {}), equalTo(new int[][] {}));
+ }
+
+ @Test
+ void findFarmland5() {
+ assertThat(new Solution().findFarmland(null), equalTo(new int[][] {}));
+ }
+}