Added solution to ch4-2 and associated tests.

Author: diadical

src/chapter4/ch4-q02.js

@@ -0,0 +1,22 @@
+'use strict';
+import { Tree } from './helpers';
+
+function add(tree, values, start, end) {
+  if (start === end) {
+    tree.add(values[start]);
+  }
+  else if (start < end) {
+    let mid = start + Math.floor((end - start) / 2);
+    tree.add(values[mid]);
+    add(tree, values, start, mid - 1);
+    add(tree, values, mid + 1, end);
+  }
+}
+
+export function makeBalancedTree(values) {
+  let tree = new Tree();
+  if (values && values.length) {
+    add(tree, values, 0, values.length - 1);
+  }
+  return tree;
+}

src/chapter4/ch4-q02.spec.js

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+import { expect } from 'chai';
+import * as helpers from './helpers';
+import * as funcs from './ch4-q02';
+
+for (let key in funcs) {
+  let func = funcs[key];
+
+  describe('ch4-q02: ' + key, function() {
+
+    it('returns empty tree with no values', function() {
+      let tree = func(null);
+      expect(tree.root).to.be.null;
+      tree = func([]);
+      expect(tree.root).to.be.null;
+    });
+
+    it('returns tree with root node set with one value', function() {
+      let tree = func([10]);
+      expect(tree.root.val).to.equal(10);
+    });
+
+    it('returns a balanced tree with 10 nodes', function() {
+      let tree = func([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
+      expect(helpers.isBalanced(tree)).to.be.true;
+    });
+
+    it('returns a balanced tree with 13 nodes', function() {
+      let tree = func([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]);
+      expect(helpers.isBalanced(tree)).to.be.true;
+    });
+
+    it('returns a balanced tree with 255 nodes', function() {
+      let values = [];
+      for (let i = 1; i <= 255; ++i) {
+        values.push(i);
+      }
+      let tree = func(values);
+      expect(helpers.isBalanced(tree)).to.be.true;
+    });
+
+  });
+
+}