fix(sorts): stop SwapSort looping forever on duplicate values (#7660)

Co-authored-by: Oleksandr Klymenko <19151554+alxkm@users.noreply.github.com>

Author: Rishavbhattarai

src/main/java/com/thealgorithms/sorts/SwapSort.java

@@ -17,7 +17,12 @@ public <T extends Comparable<T>> T[] sort(T[] array) {
             final int amountSmallerElements = this.getSmallerElementCount(array, index);
 
             if (amountSmallerElements > 0) {
-                SortUtils.swap(array, index, index + amountSmallerElements);
+                int target = index + amountSmallerElements;
+                // Skip slots that already hold an equal element, otherwise two equal values swap forever
+                while (array[target].compareTo(array[index]) == 0) {
+                    target++;
+                }
+                SortUtils.swap(array, index, target);
             } else {
                 index++;
             }

src/test/java/com/thealgorithms/sorts/SwapSortTest.java

@@ -1,8 +1,21 @@
 package com.thealgorithms.sorts;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+
+import java.util.concurrent.TimeUnit;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
+
 public class SwapSortTest extends SortingAlgorithmTest {
     @Override
     SortAlgorithm getSortAlgorithm() {
         return new SwapSort();
     }
+
+    @Test
+    @Timeout(value = 1, unit = TimeUnit.SECONDS, threadMode = Timeout.ThreadMode.SEPARATE_THREAD)
+    void shouldSortWhenDuplicateWouldBeSwappedOntoItsTwin() {
+        Integer[] array = {2, 2, 1, 1, 0, 0, 0};
+        assertArrayEquals(new Integer[] {0, 0, 0, 1, 1, 2, 2}, new SwapSort().sort(array));
+    }
 }