From bcb0f25a1d8f0472d092e228ff28ad9059666e0e Mon Sep 17 00:00:00 2001
From: me <me@fymio.us>
Date: Tue, 17 Feb 2026 13:47:22 +0300
Subject: [PATCH] update README.md + update tests + add solution for hw2:3839

---
 .gitea/workflows/search.yml           |   2 +-
 README.md                             |   8 +++
 artifacts/search/BinarySearchTest.jar | Bin 31876 -> 32033 bytes
 java/search/BinarySearch3839.java     |  77 ++++++++++++++++++++++++++
 java/search/BinarySearchTest.java     |  10 ++++
 5 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 java/search/BinarySearch3839.java

diff --git a/.gitea/workflows/search.yml b/.gitea/workflows/search.yml
index 49ea77a..0b136ba 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 3637
+          java -ea -cp out search.BinarySearchTest Base 3637 3839
diff --git a/README.md b/README.md
index 012a26e..d0b8bec 100644
--- a/README.md
+++ b/README.md
@@ -15,6 +15,14 @@
 	* Требуется вывести число элементов массива, равных `x`.
 	* Не допускается использование типов `long` и `BigInteger`.
 	* Класс должен иметь имя `BinarySearch3637`
+*  *3839* ✅
+    * На вход подаётся число `x` и массив, отсортированный по невозрастанию.
+    * Требуется вывести два числа: начало и длину диапазона элементов, равных `x`.
+      Если таких элементов нет, то следует вывести
+      пустой диапазон, у которого левая граница совпадает с местом
+      вставки элемента `x`.
+    * Не допускается использование типов `long` и `BigInteger`.
+    * Класс должен иметь имя `BinarySearch3839`
 
 
 <!--
diff --git a/artifacts/search/BinarySearchTest.jar b/artifacts/search/BinarySearchTest.jar
index b463045521e53d3f3f62ff6408daf58b15423961..6956f8b82e96cd0908cc2a39028c5f58b2ed8cb4 100644
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diff --git a/java/search/BinarySearch3839.java b/java/search/BinarySearch3839.java
new file mode 100644
index 0000000..269ca0f
--- /dev/null
+++ b/java/search/BinarySearch3839.java
@@ -0,0 +1,77 @@
+package search;
+
+/**
+ * @author Nikita Doschennikov (me@fymio.us)
+ */
+public class BinarySearch3839 {
+
+    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]));
+        }
+
+        int leftBound = leftBoundIterative(x, a);
+        int rightBound = rightBoundIterative(x, a);
+        int range = rightBound - leftBound;
+        System.out.println(leftBound + " " + range);
+    }
+
+    static int leftBoundIterative(int x, IntList a) {
+        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 high + 1;
+    }
+
+    static int rightBoundIterative(int x, IntList a) {
+        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 high + 1;
+    }
+
+    static int leftBoundRecursive(int x, IntList a, int low, int high) {
+        if (low > high) {
+            return high + 1;
+        }
+
+        int mid = low + (high - low) / 2;
+
+        if (a.get(mid) > x) {
+            return leftBoundRecursive(x, a, mid + 1, high);
+        } else {
+            return leftBoundRecursive(x, a, low, mid - 1);
+        }
+    }
+
+    static int rightBoundRecursive(int x, IntList a, int low, int high) {
+        if (low > high) {
+            return high + 1;
+        }
+
+        int mid = low + (high - low) / 2;
+
+        if (a.get(mid) >= x) {
+            return rightBoundRecursive(x, a, mid + 1, high);
+        } else {
+            return rightBoundRecursive(x, a, low, mid - 1);
+        }
+    }
+}
diff --git a/java/search/BinarySearchTest.java b/java/search/BinarySearchTest.java
index e848955..10e2f2c 100644
--- a/java/search/BinarySearchTest.java
+++ b/java/search/BinarySearchTest.java
@@ -37,11 +37,21 @@ public final class BinarySearchTest {
     }
 
 
+    // === 3839
+
+    private static String span(final int c, final int x, final int[] a) {
+        final int begin = range(0, a.length).filter(i -> a[i] == x || Integer.compare(x, a[i]) == c).findFirst().orElse(a.length);
+        final long length = range(0, a.length).filter(i -> a[i] == x).count();
+        return begin + " " + length;
+    }
+
+
     // === 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))
+            .variant("3839",    Solver.variant0("3839", Kind.DESC,  BinarySearchTest::span))
             ;
 
     public static void main(final String... args) {