add 3637 mod + tests

.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

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

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);
+        }
+    }
+}

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) {

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];
     }