Move solution to src/huffman.js

Author: Syeoryn

SpecRunner.html

@@ -18,7 +18,7 @@
     <!-- Load tests and helpers here -->
     <script src="src/priorityQueue.js"></script>
     <script src="src/misc.js"></script>
-    <script src="solution/solution.js"></script>
+    <script src="src/huffman.js"></script>
     <script src="spec/spec.js"></script>
 
     <script>

src/huffman.js

@@ -1,13 +1,43 @@
-// // Given a Huffman tree and a string, encode that string into a new string
-// // consisting only of 1s and 0s, using the code given by the tree.
-var encodeString = function(input, huffmanTree) {
-  return "Not implemented yet!";
+// Given a Huffman tree and a string, encode that string into a new string
+// consisting only of 1s and 0s, using the code given by the tree.
+var encodeString = function(input, huffman) {
+  var output = "";
+  for (var i = 0; i < input.length; i++) {
+    var currentNode = huffman;
+    var nextCharacter = input[i];
+    while (currentNode.val.length > 1) {
+      if (currentNode.left.val.indexOf(nextCharacter) !== -1) {
+        currentNode = currentNode.left;
+        output += "0";
+      } else if (currentNode.right.val.indexOf(nextCharacter) !== -1) {
+        currentNode = currentNode.right;
+        output += "1";
+      } else {
+        throw new Error("Character " + nextCharacter + " is not in this Huffman tree.");
+      }
+    }
+  }
+  return output;
 };
 
-// // Given a Huffman tree and a string of 1s and 0s, decode that string into
-// // a new, human-readable string, using the code given by the tree.
-var decodeString = function(input, huffmanTree) {
-  return "Not implemented yet!";
+// Given a Huffman tree and a string of 1s and 0s, decode that string into
+// a new, human-readable string, using the code given by the tree.
+var decodeString = function(input, huffman) {
+  var output = "";
+  var currNode = huffman;
+  for (var currIdx = 0; currIdx < input.length; currIdx++) {
+    var currBit = input[currIdx];
+    if (currBit === "0") {
+      currNode = currNode.left;
+    } else if (currBit === "1") {
+      currNode = currNode.right;
+    }
+    if (currNode.val.length === 1) {
+      output += currNode.val[0];
+      currNode = huffman;
+    }
+  }
+  return output;
 };
 
 // Given a corpus of text, return a Huffman tree that represents the
@@ -22,7 +52,39 @@ var decodeString = function(input, huffmanTree) {
 // You may also use the `Tree` class that is provided in the file `misc.js`
 // Some corpuses are included as the variables `lorumIpsum` and `declaration`.
 var makeHuffmanTree = function(corpus) {
-  alert("You must implement makeHuffmanTree first!")
-  return new Tree();
+  var charCounts = countChars(corpus);
+  var pq = new PriorityQueue();
+  for (var c in charCounts) {
+    var n = charCounts[c];
+    var tree = new Tree([c]);
+    pq.insert(n, tree);
+  }
+
+  while (pq.size() > 1) {
+    var first = pq.extract();
+    var second = pq.extract();
+
+    var tree1 = first.val;
+    var tree2 = second.val;
+
+    var key1 = first.key;
+    var key2 = second.key;
+
+    var newTree = new Tree(tree1.val.concat(tree2.val));
+    newTree.left = tree1;
+    newTree.right = tree2;
+    pq.insert(key1+key2, newTree);
+  }
+
+  return pq.extract().val;
 };
 
+var countChars = function(input) {
+  var counts = {};
+  for (var i = 0; i < input.length; i++) {
+    var c = input[i];
+    counts[c] = counts[c] || 0;
+    counts[c]++;
+  }
+  return counts;
+};