From e8e085e606bfacdd3b7c6ed29647f8f681dd663f Mon Sep 17 00:00:00 2001
From: me <me@fymio.us>
Date: Tue, 17 Feb 2026 12:57:43 +0300
Subject: [PATCH] add 3637 mod + tests

---
 .gitea/workflows/search.yml           |   2 +-
 README.md                             |   6 ++
 artifacts/search/BinarySearchTest.jar | Bin 31747 -> 31876 bytes
 java/search/BinarySearch3637.java     |  88 ++++++++++++++++++++++++++
 java/search/BinarySearchTest.java     |  10 +++
 java/search/IntList.java              |  14 ++++
 6 files changed, 119 insertions(+), 1 deletion(-)
 create mode 100644 java/search/BinarySearch3637.java

diff --git a/.gitea/workflows/search.yml b/.gitea/workflows/search.yml
index faeb097..49ea77a 100644
--- a/.gitea/workflows/search.yml
+++ b/.gitea/workflows/search.yml
@@ -14,4 +14,4 @@ jobs:
           javac -d out $(find java common -name "*.java")
       - name: Run Binary Search tests
         run: |
-          java -ea -cp out search.BinarySearchTest Base
+          java -ea -cp out search.BinarySearchTest Base 3637
diff --git a/README.md b/README.md
index d4bd549..57b4ac6 100644
--- a/README.md
+++ b/README.md
@@ -10,6 +10,12 @@
     * Класс `BinarySearch` должен находиться в пакете `search`
     * [Исходный код тестов](java/search/BinarySearchTest.java)
     * [Откомпилированные тесты](artifacts/search/BinarySearchTest.jar)
+ * *3637*
+	    * На вход подаётся число `x` и массив, отсортированный по невозрастанию.
+	    * Требуется вывести число элементов массива, равных `x`.
+	    * Не допускается использование типов `long` и `BigInteger`.
+	    * Класс должен иметь имя `BinarySearch3637`
+
 
 <!--
 ## Домашнее задание 1. Обработка ошибок
diff --git a/artifacts/search/BinarySearchTest.jar b/artifacts/search/BinarySearchTest.jar
index 47c113f53b26df92b0d43482db48299bb959cfaf..b463045521e53d3f3f62ff6408daf58b15423961 100644
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diff --git a/java/search/BinarySearch3637.java b/java/search/BinarySearch3637.java
new file mode 100644
index 0000000..713347c
--- /dev/null
+++ b/java/search/BinarySearch3637.java
@@ -0,0 +1,88 @@
+package search;
+
+/**
+ * @author Nikita Doschennikov (me@fymio.us)
+ */
+public class BinarySearch3637 {
+
+    public static void main(String[] args) {
+        IntList a = new IntList();
+        int x = Integer.parseInt(args[0]);
+
+        int n = args.length;
+
+        for (int i = 1; i < n; i++) {
+            a.put(Integer.parseInt(args[i]));
+        }
+
+        System.out.println(
+            searchIterativeIncreasing(x, a.getReversed()) -
+                searchIterativeDecreasing(x, a)
+        );
+    }
+
+    static int searchIterativeIncreasing(int x, IntList a) {
+        if (a.getLength() == 0) {
+            return 0;
+        }
+
+        int low = 0,
+            high = a.getLength() - 1;
+
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+
+            if (a.get(mid) <= x) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+
+        return low;
+    }
+
+    static int searchIterativeDecreasing(int x, IntList a) {
+        if (a.getLength() == 0) {
+            return 0;
+        }
+
+        int low = 0,
+            high = a.getLength() - 1;
+
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+
+            if (a.get(mid) <= x) {
+                high = mid - 1;
+            } else {
+                low = mid + 1;
+            }
+        }
+
+        return low;
+    }
+
+    static int searchRecursive(int x, IntList a) {
+        return searchRecursiveHelper(x, a, 0, a.getLength() - 1);
+    }
+
+    private static int searchRecursiveHelper(
+        int x,
+        IntList a,
+        int low,
+        int high
+    ) {
+        if (low > high) {
+            return low;
+        }
+
+        int mid = low + (high - low) / 2;
+
+        if (a.get(mid) <= x) {
+            return searchRecursiveHelper(x, a, low, mid - 1);
+        } else {
+            return searchRecursiveHelper(x, a, mid + 1, high);
+        }
+    }
+}
diff --git a/java/search/BinarySearchTest.java b/java/search/BinarySearchTest.java
index 3410b9b..e848955 100644
--- a/java/search/BinarySearchTest.java
+++ b/java/search/BinarySearchTest.java
@@ -12,6 +12,8 @@ import java.util.function.Function;
 import java.util.stream.IntStream;
 import java.util.stream.Stream;
 
+import static java.util.stream.IntStream.range;
+
 /**
  * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
  */
@@ -28,10 +30,18 @@ public final class BinarySearchTest {
     }
 
 
+    // === 3637
+
+    private static int count(final int c, final int x, final int[] a) {
+        return (int) range(0, a.length).filter(i -> a[i] == x).count();
+    }
+
+
     // === Common code
 
     public static final Selector SELECTOR = new Selector(BinarySearchTest.class)
             .variant("Base",    Solver.variant0("", Kind.DESC, BinarySearchTest::base))
+            .variant("3637",    Solver.variant0("3637", Kind.DESC,  BinarySearchTest::count))
             ;
 
     public static void main(final String... args) {
diff --git a/java/search/IntList.java b/java/search/IntList.java
index c86ee4e..8801fa6 100644
--- a/java/search/IntList.java
+++ b/java/search/IntList.java
@@ -12,6 +12,10 @@ public class IntList {
 
     public IntList() {}
 
+    public IntList(int[] list) {
+        this.list = list;
+    }
+
     public void put(int val) {
         if (idx >= list.length) {
             list = Arrays.copyOf(list, list.length * 2);
@@ -24,6 +28,16 @@ public class IntList {
         return idx;
     }
 
+    public IntList getReversed() {
+        IntList reverse = new IntList(new int[idx]);
+
+        for (int i = idx - 1; i >= 0; i--) {
+            reverse.put(list[i]);
+        }
+
+        return reverse;
+    }
+
     public int get(int index) {
         return list[index];
     }