4.5 is a binary search tree.js - works for most cases but ONE

Author: amejiarosario

src/trees-and-graphs/graph.js

@@ -10,6 +10,22 @@ class Node {
     this.visited = false;
   }
 
+  get left() {
+    return this.adjacents[0];
+  }
+
+  set left(value) {
+    this.adjacents[0] = value;
+  }
+
+  get right() {
+    return this.adjacents[1];
+  }
+
+  set right(value) {
+    this.adjacents[1] = value;
+  }
+
   toArray() {
     const string = [];
     const queue = new Queue();

src/trees-and-graphs/is-binary-search-tree.js

@@ -0,0 +1,25 @@
+/**
+ * DFS, where the left be in desc while the right should be asc
+ * @param node
+ * @returns {boolean}
+ */
+function isBinarySearchTree(node) {
+  if(!node) return true;
+
+  const parent = node.data;
+  let isBST = true;
+
+  if(node.left) {
+    const left = node.left.data;
+    isBST = isBST && left < parent;
+  }
+
+  if(node.right) {
+    const right = node.right.data;
+    isBST = isBST && right > parent;
+  }
+
+  return isBST && isBinarySearchTree(node.left) && isBinarySearchTree(node.right);
+}
+
+module.exports = isBinarySearchTree;

src/trees-and-graphs/is-binary-search-tree.spec.js

@@ -0,0 +1,63 @@
+const expect = require('chai').expect;
+const Node = require('./graph').Node;
+const isBinarySearchTree = require('./is-binary-search-tree');
+
+describe('Tree: is binary tree search', function () {
+
+  it('should work with valid data', function () {
+    let bt = new Node(4);
+    bt.left = new Node(2);
+    bt.right = new Node(5);
+    expect(isBinarySearchTree(bt)).to.equal(true);
+  });
+
+  it('should false with left > parent', function () {
+    let bt = new Node(4);
+    bt.left = new Node(6);
+    bt.right = new Node(5);
+    expect(isBinarySearchTree(bt)).to.equal(false);
+  });
+
+  it('should false with parent > right', function () {
+    let bt = new Node(4);
+    bt.left = new Node(2);
+    bt.right = new Node(3);
+    expect(isBinarySearchTree(bt)).to.equal(false);
+  });
+
+  it('should work with valid data', function () {
+    let
+      a = new Node('a'),
+      b = new Node('b'),
+      c = new Node('c'),
+      d = new Node('d'),
+      e = new Node('e'),
+      f = new Node('f'),
+      g = new Node('g');
+
+    d.left = c;
+    c.left = b;
+
+    d.right = e;
+    e.right = f;
+    f.right = g;
+
+    expect(isBinarySearchTree(d)).to.equal(true);
+  });
+
+  it('should return false when the left child is bigger than root', function () {
+    let
+      n10 = new Node(10),
+      n20 = new Node(20),
+      n25 = new Node(25),
+      n30 = new Node(30);
+
+    n20.left = n10;
+    n20.right = n30;
+
+    n10.right = n25;
+
+    expect(isBinarySearchTree(n20)).to.equal(false);
+  });
+
+});