Added Huffman Coding.

huffman_coding/src/huffman_coding/Main.java

@@ -0,0 +1,46 @@
+package huffman_coding;
+
+import java.util.ArrayList;
+import tester.Tester;
+
+class Examples {
+
+    void testTest(Tester t) {
+        t.checkExpect(1, 1);
+    }
+}
+
+class Huffman {
+
+    ArrayList<String> charset; // Character set.
+    ArrayList<Boolean> freqs; // Relative frequencies of characters.
+
+    Huffman(ArrayList<String> charset, ArrayList<Boolean> freqs) {
+        if (charset.size() != freqs.size()) throw new IllegalArgumentException(
+            "Character set must match frequencies."
+        );
+
+        if (charset.size() < 2) throw new IllegalArgumentException(
+            "Character set too small."
+        );
+
+        this.charset = charset;
+        this.freqs = freqs;
+    }
+}
+
+// Binary tree.
+interface ITree<T> {}
+
+class Node<T> implements ITree<T> {
+
+    ITree<T> l;
+    ITree<T> r;
+
+    Node(ITree<T> l, ITree<T> r) {
+        this.l = l;
+        this.r = r;
+    }
+}
+
+class Leaf<T> implements ITree<T> {}