Count distincts in every sub-array

Chapter10/CountDistinctInSubarray/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>coding.challenge</groupId>
+    <artifactId>CountDistinctInSubarray</artifactId>
+    <version>1.0</version>
+    <packaging>jar</packaging>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>13</maven.compiler.source>
+        <maven.compiler.target>13</maven.compiler.target>
+    </properties>
+    <name>CountDistinctInSubarray</name>
+</project>

Chapter10/CountDistinctInSubarray/src/main/java/coding/challenge/Arrays.java

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+package coding.challenge;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public final class Arrays {
+
+    private Arrays() {
+        throw new AssertionError("Cannot be instantiated");
+    }
+
+    public static void find(int[] m, int n) {
+
+        if (m == null) {
+            throw new IllegalArgumentException("The given array cannot be null");
+        }
+
+        if (n <= 0) {
+            throw new IllegalArgumentException("The given sub-array size cannot be <= 0");
+        }
+
+        // store frequency of elements in current window of size n
+        Map<Integer, Integer> frequency = new HashMap<>();
+
+        // count distinct elements in every sub-array of size n
+        int countDistinct = 0;
+
+        for (int i = 0; i < m.length; i++) {
+
+            // skip first n elements
+            if (i >= n) {
+                // Remove first element from the sub-array
+                frequency.putIfAbsent(m[i - n], 0);
+                frequency.put(m[i - n], frequency.get(m[i - n]) - 1);
+
+                // reduce distinct count if we are left with 0
+                if (frequency.get(m[i - n]) == 0) {
+                    countDistinct--;
+                }
+            }
+
+            // add current element to the sub-array 
+            frequency.putIfAbsent(m[i], 0);
+            frequency.put(m[i], frequency.get(m[i]) + 1);
+
+            // element is for the first time in current window?
+            if (frequency.get(m[i]) == 1) {
+                countDistinct++;
+            }
+
+            if (i >= n - 1) {
+                System.out.println("Distinct elements in the "
+                        + "sub-array [" + (i - n + 1) + ", " + i + "]" + " is "
+                        + countDistinct);
+            }
+        }
+    }
+}

Chapter10/CountDistinctInSubarray/src/main/java/coding/challenge/Main.java

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+package coding.challenge;
+
+public class Main {
+
+    public static void main(String[] args) {
+
+        int[] m = {7, 11, 11, -5, 13, 13, 13, 15, -4, -3, -4, 15, -2, 0, 0, 0, 14, 3, 7, 42, 3};
+        int k = 5;
+
+        System.out.println("Array: " + java.util.Arrays.toString(m));
+
+        Arrays.find(m, k);
+    }
+}