Add LZW and Arithmetic Coding algorithms in compression category

src/main/java/com/thealgorithms/compression/ArithmeticCoding.java

@@ -0,0 +1,39 @@
+package com.thealgorithms.compression;
+
+import java.util.Map;
+
+/**
+ * Implementation of Arithmetic Coding algorithm.
+ * Reference: https://en.wikipedia.org/wiki/Arithmetic_coding
+ */
+
+public final class ArithmeticCoding {
+
+    private ArithmeticCoding() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    public static double encode(String input, Map<Character, Double> probabilities) {
+        double low = 0.0;
+        double high = 1.0;
+
+        for (char symbol : input.toCharArray()) {
+            double range = high - low;
+            double cumProb = 0.0;
+
+            for (Map.Entry<Character, Double> entry : probabilities.entrySet()) {
+                char current = entry.getKey();
+                double prob = entry.getValue();
+                double next = cumProb + prob;
+
+                if (symbol == current) {
+                    high = low + range * next;
+                    low = low + range * cumProb;
+                    break;
+                }
+                cumProb = next;
+            }
+        }
+        return (low + high) / 2.0;
+    }
+}

src/main/java/com/thealgorithms/compression/LZW.java

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+package com.thealgorithms.compression;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Implementation of LZW (Lempel–Ziv–Welch) compression algorithm.
+ * Reference: https://en.wikipedia.org/wiki/Lempel–Ziv–Welch
+ */
+
+public final class LZW {
+
+    private LZW() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    public static List<Integer> compress(String input) {
+        int dictSize = 256;
+        Map<String, Integer> dictionary = new HashMap<>();
+        for (int i = 0; i < 256; i++) {
+            dictionary.put("" + (char) i, i);
+        }
+
+        String w = "";
+        List<Integer> result = new ArrayList<>();
+
+        for (char c : input.toCharArray()) {
+            String wc = w + c;
+            if (dictionary.containsKey(wc)) {
+                w = wc;
+            } else {
+                result.add(dictionary.get(w));
+                dictionary.put(wc, dictSize++);
+                w = "" + c;
+            }
+        }
+
+        if (!w.isEmpty()) {
+            result.add(dictionary.get(w));
+        }
+
+        return result;
+    }
+}