add 3643

Author: fishercoder1534

paginated_contents/algorithms/4th_thousand/README.md

@@ -69,6 +69,7 @@
 | 3668 | [Restore Finishing Order](https://leetcode.com/problems/restore-finishing-order/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3668.java) |                                                                               | Easy       |
 | 3663 | [Find The Least Frequent Digit](https://leetcode.com/problems/find-the-least-frequent-digit/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3663.java) |                                                                               | Easy       |
 | 3662 | [Filter Characters by Frequency](https://leetcode.com/problems/filter-characters-by-frequency/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3662.java) |                                                                               | Easy       |
+| 3643 | [Flip Square Submatrix Vertically](https://leetcode.com/problems/flip-square-submatrix-vertically/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3643.java) |                                                                               | Easy       |
 | 3622 | [Check Divisibility by Digit Sum and Product](https://leetcode.com/problems/check-divisibility-by-digit-sum-and-product/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3622.java) |                                                                               | Easy       | 
 | 3608 | [Minimum Time for K Connected Components](https://leetcode.com/problems/minimum-time-for-k-connected-components/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3608.java) |                                                                               | Medium     | UnionFind
 | 3606 | [Coupon Code Validator](https://leetcode.com/problems/coupon-code-validator/)                                                               | [Java](https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/fourththousand/_3606.java) |                                                                               | Easy       |

src/main/java/com/fishercoder/solutions/fourththousand/_3643.java

@@ -0,0 +1,23 @@
+package com.fishercoder.solutions.fourththousand;
+
+public class _3643 {
+    public static class Solution1 {
+        public int[][] reverseSubmatrix(int[][] grid, int x, int y, int k) {
+            int top = x;
+            int bottom = x + k - 1;
+            int rightBoundary = y + k - 1;
+            while (top < bottom) {
+                int left = y;
+                while (left <= rightBoundary) {
+                    int temp = grid[top][left];
+                    grid[top][left] = grid[bottom][left];
+                    grid[bottom][left] = temp;
+                    left++;
+                }
+                top++;
+                bottom--;
+            }
+            return grid;
+        }
+    }
+}

src/test/java/com/fishercoder/fourththousand/_3643Test.java

@@ -0,0 +1,28 @@
+package com.fishercoder.fourththousand;
+
+import com.fishercoder.common.utils.CommonUtils;
+import com.fishercoder.solutions.fourththousand._3643;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+public class _3643Test {
+    private _3643.Solution1 solution1;
+
+    @BeforeEach
+    public void setup() {
+        solution1 = new _3643.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertArrayEquals((CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[1,2,3,4],[13,14,15,8],[9,10,11,12],[5,6,7,16]")), solution1.reverseSubmatrix(CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[1,2,3,4],[5,6,7,8],[9,10,11,12],[13,14,15,16]"), 1, 0, 3));
+    }
+
+    @Test
+    public void test2() {
+        assertArrayEquals((CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[11,15,18,6],[19,19,4,15],[2,14,11,20],[14,3,18,16]")), solution1.reverseSubmatrix(CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[14,3,18,16],[2,14,11,20],[19,19,4,15],[11,15,18,6]"), 0, 0, 4));
+    }
+
+}