feat: add Huffman Coding greedy algorithm implementation

Author: putku45

src/main/java/com/thealgorithms/greedyalgorithms/HuffmanCoding.java

@@ -0,0 +1,47 @@
+package com.thealgorithms.greedyalgorithms;
+
+import java.util.PriorityQueue;
+
+/**
+ * Huffman Coding Algorithm
+ * Greedy algorithm used for optimal prefix codes.
+ */
+public class HuffmanCoding {
+
+    static class Node implements Comparable<Node> {
+        char character;
+        int frequency;
+        Node left;
+        Node right;
+
+        Node(char character, int frequency) {
+            this.character = character;
+            this.frequency = frequency;
+        }
+
+        public int compareTo(Node other) {
+            return this.frequency - other.frequency;
+        }
+    }
+
+    public static Node buildHuffmanTree(char[] chars, int[] freq) {
+        PriorityQueue<Node> pq = new PriorityQueue<>();
+
+        for (int i = 0; i < chars.length; i++) {
+            pq.add(new Node(chars[i], freq[i]));
+        }
+
+        while (pq.size() > 1) {
+            Node left = pq.poll();
+            Node right = pq.poll();
+
+            Node parent = new Node('\0', left.frequency + right.frequency);
+            parent.left = left;
+            parent.right = right;
+
+            pq.add(parent);
+        }
+
+        return pq.poll();
+    }
+}