From e02e519b2c630d1cd40e6397d1030774108c71aa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=D0=90=D1=80=D1=82=D1=8E=D1=89=D0=B8=D0=BA=20=D0=90=D0=BD?=
 =?UTF-8?q?=D0=B0=D1=81=D1=82=D0=B0=D1=81=D0=B8=D1=8F?=
 <nastya.2012.v@yandex.ru>
Date: Sat, 29 Aug 2026 12:47:02 +0300
Subject: [PATCH] feat(sorting): add even-only sort strategy

---
 .../project/sorting/EvenOnlySortStrategy.java | 94 +++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 app/src/main/java/ru/project/sorting/EvenOnlySortStrategy.java

diff --git a/app/src/main/java/ru/project/sorting/EvenOnlySortStrategy.java b/app/src/main/java/ru/project/sorting/EvenOnlySortStrategy.java
new file mode 100644
index 0000000..32349c1
--- /dev/null
+++ b/app/src/main/java/ru/project/sorting/EvenOnlySortStrategy.java
@@ -0,0 +1,94 @@
+package ru.project.sorting;
+
+import ru.project.collection.MyLinkedList;
+import ru.project.collection.MyList;
+
+import java.util.Comparator;
+import java.util.function.ToIntFunction;
+
+public class EvenOnlySortStrategy<T> implements SortStrategy<T> {
+
+    private SortStrategy<T> sortStrategy;
+    private ToIntFunction<T> valueExtractor;
+
+    public EvenOnlySortStrategy() {
+    }
+
+    public EvenOnlySortStrategy(SortStrategy<T> sortStrategy) {
+        setSortStrategy(sortStrategy);
+    }
+
+    public EvenOnlySortStrategy(
+            SortStrategy<T> sortStrategy,
+            ToIntFunction<T> valueExtractor
+    ) {
+        setSortStrategy(sortStrategy);
+        setValueExtractor(valueExtractor);
+    }
+
+    public void setSortStrategy(SortStrategy<T> sortStrategy) {
+        if (sortStrategy == null) {
+            throw new IllegalArgumentException("Sort strategy must not be null");
+        }
+
+        this.sortStrategy = sortStrategy;
+    }
+
+    public void setValueExtractor(ToIntFunction<T> valueExtractor) {
+        if (valueExtractor == null) {
+            throw new IllegalArgumentException("Value extractor must not be null");
+        }
+
+        this.valueExtractor = valueExtractor;
+    }
+
+    @Override
+    public void sort(MyList<T> list, Comparator<T> comparator) {
+        if (sortStrategy == null) {
+            throw new IllegalStateException("Sort strategy is not set");
+        }
+
+        if (valueExtractor == null) {
+            throw new IllegalStateException("Value extractor is not set");
+        }
+
+        if (list == null || list.size() <= 1) {
+            return;
+        }
+
+        int evenCount = 0;
+
+        for (int i = 0; i < list.size(); i++) {
+            T element = list.get(i);
+
+            if (valueExtractor.applyAsInt(element) % 2 == 0) {
+                evenCount++;
+            }
+        }
+
+        if (evenCount <= 1) {
+            return;
+        }
+
+        MyList<T> evenElements = new MyLinkedList<>();
+        int[] evenIndexes = new int[evenCount];
+
+        int evenIndex = 0;
+
+        for (int i = 0; i < list.size(); i++) {
+            T element = list.get(i);
+
+            if (valueExtractor.applyAsInt(element) % 2 == 0) {
+                evenElements.add(element);
+                evenIndexes[evenIndex] = i;
+                evenIndex++;
+            }
+        }
+
+        sortStrategy.sort(evenElements, comparator);
+
+        for (int i = 0; i < evenIndexes.length; i++) {
+            list.set(evenIndexes[i], evenElements.get(i));
+        }
+    }
+}
\ No newline at end of file