From 78ac11c435db62f9c3b59a76f8cff25dc7b4c984 Mon Sep 17 00:00:00 2001
From: Rishavbhattarai <bhattarai.rishav@gmail.com>
Date: Mon, 26 Oct 2026 19:25:02 -0700
Subject: [PATCH] fix(sorts): handle small arrays in FlashSort and empty arrays
 in DutchNationalFlagSort

---
 .../com/thealgorithms/sorts/DutchNationalFlagSort.java     | 3 +++
 src/main/java/com/thealgorithms/sorts/FlashSort.java       | 3 ++-
 .../com/thealgorithms/sorts/DutchNationalFlagSortTest.java | 6 ++++++
 src/test/java/com/thealgorithms/sorts/FlashSortTest.java   | 7 +++++++
 4 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java b/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java
index f7e12da06568..2e3a2fcea704 100644
--- a/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java
+++ b/src/main/java/com/thealgorithms/sorts/DutchNationalFlagSort.java
@@ -13,6 +13,9 @@ public class DutchNationalFlagSort implements SortAlgorithm {
 
     @Override
     public <T extends Comparable<T>> T[] sort(T[] array) {
+        if (array.length == 0) {
+            return array;
+        }
         return dutchNationalFlagSort(array, array[(int) Math.ceil((array.length) / 2.0) - 1]);
     }
 
diff --git a/src/main/java/com/thealgorithms/sorts/FlashSort.java b/src/main/java/com/thealgorithms/sorts/FlashSort.java
index e8dbf8c42742..79c2d8b82700 100644
--- a/src/main/java/com/thealgorithms/sorts/FlashSort.java
+++ b/src/main/java/com/thealgorithms/sorts/FlashSort.java
@@ -76,7 +76,8 @@ private <T extends Comparable<? super T>> void flashSort(T[] arr) {
             return; // All elements are the same
         }
 
-        final int m = (int) (classificationRatio * arr.length);
+        // At least one class, otherwise small arrays index into an empty classification table
+        final int m = Math.max(1, (int) (classificationRatio * arr.length));
 
         final int[] classificationArray = new int[m];
 
diff --git a/src/test/java/com/thealgorithms/sorts/DutchNationalFlagSortTest.java b/src/test/java/com/thealgorithms/sorts/DutchNationalFlagSortTest.java
index c7581e7c8f7b..d9c014e8b21d 100644
--- a/src/test/java/com/thealgorithms/sorts/DutchNationalFlagSortTest.java
+++ b/src/test/java/com/thealgorithms/sorts/DutchNationalFlagSortTest.java
@@ -109,4 +109,10 @@ void testOddStringsMidGivenDnfs() {
         dutchNationalFlagSort.sort(strings, "e");
         assertArrayEquals(strings, stringsResult);
     }
+
+    @Test
+    void testEmptyArray() {
+        Integer[] integers = {};
+        assertArrayEquals(new Integer[] {}, new DutchNationalFlagSort().sort(integers));
+    }
 }
diff --git a/src/test/java/com/thealgorithms/sorts/FlashSortTest.java b/src/test/java/com/thealgorithms/sorts/FlashSortTest.java
index 5b27975d3bea..6b4b1230925f 100644
--- a/src/test/java/com/thealgorithms/sorts/FlashSortTest.java
+++ b/src/test/java/com/thealgorithms/sorts/FlashSortTest.java
@@ -1,5 +1,6 @@
 package com.thealgorithms.sorts;
 
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
@@ -59,6 +60,12 @@ public List<DynamicTest> dynamicTestsForSorting() {
         return dynamicTests;
     }
 
+    @Test
+    public void testArraysTooSmallForMoreThanOneClass() {
+        assertArrayEquals(new Integer[] {1, 2}, new FlashSort().sort(new Integer[] {2, 1}));
+        assertArrayEquals(new Integer[] {1, 2, 3, 4, 5}, new FlashSort(0.1).sort(new Integer[] {5, 3, 1, 4, 2}));
+    }
+
     private List<DynamicTest> createDynamicTestsForRatio(double ratio) {
         List<DynamicTest> dynamicTests = new ArrayList<>();
         for (TestMethod testMethod : getTestMethodsFromSuperClass()) {