Add Spiral Matrix II algorithm

Author: itsKomal1508

src/main/java/com/thealgorithms/matrix/SpiralMatrixII.java

@@ -0,0 +1,43 @@
+package com.thealgorithms.matrix;
+
+public class SpiralMatrixII {
+
+    public int[][] generateMatrix(int n) {
+
+        int[][] matrix = new int[n][n];
+
+        int top = 0, bottom = n - 1;
+        int left = 0, right = n - 1;
+
+        int num = 1;
+
+        while (top <= bottom && left <= right) {
+
+            for (int i = left; i <= right; i++) {
+                matrix[top][i] = num++;
+            }
+            top++;
+
+            for (int i = top; i <= bottom; i++) {
+                matrix[i][right] = num++;
+            }
+            right--;
+
+            if (top <= bottom) {
+                for (int i = right; i >= left; i--) {
+                    matrix[bottom][i] = num++;
+                }
+                bottom--;
+            }
+
+            if (left <= right) {
+                for (int i = bottom; i >= top; i--) {
+                    matrix[i][left] = num++;
+                }
+                left++;
+            }
+        }
+
+        return matrix;
+    }
+}

src/test/java/com/thealgorithms/matrix/SpiralMatrixIITest.java

@@ -0,0 +1,37 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import org.junit.jupiter.api.Test;
+
+class SpiralMatrixIITest {
+
+    private final SpiralMatrixII spiral = new SpiralMatrixII();
+
+    @Test
+    void testNEquals1() {
+        int[][] expected = {{1}};
+        assertArrayEquals(expected, spiral.generateMatrix(1));
+    }
+
+    @Test
+    void testNEquals3() {
+        int[][] expected = {
+            {1, 2, 3},
+            {8, 9, 4},
+            {7, 6, 5}
+        };
+        assertArrayEquals(expected, spiral.generateMatrix(3));
+    }
+
+    @Test
+    void testNEquals4() {
+        int[][] expected = {
+            {1, 2, 3, 4},
+            {12, 13, 14, 5},
+            {11, 16, 15, 6},
+            {10, 9, 8, 7}
+        };
+        assertArrayEquals(expected, spiral.generateMatrix(4));
+    }
+}