Minor revisions

Author: awpala

javascript/algorithm-techniques/p431_HuffmanCodes.js

@@ -36,7 +36,7 @@ const huffman = (C) => {
     const n = Object.keys(C).length;
     const Q = new HuffmanMinPQ(C);
     for (let i = 1; i < n; i++) {
-        let z = new CharNode(null);
+        let z = new CharNode(null); // N.B. null/non-key for tree nodes
         let x = z.left = Q.extractMin();
         let y = z.right = Q.extractMin();
         z.freq = x.freq + y.freq;

javascript/utilities.js

@@ -32,7 +32,7 @@ class RBTreeNode extends TreeNode {
 }
 
 class CharNode {
-    constructor(char = null, freq = 0, left = null, right = null) {
+    constructor(char, freq = 0, left = null, right = null) {
         this.char = char;
         this.freq = freq;
         this.left = left;