Chapter 19: Binary Trees Java Programming: Program Design Including Data Structures Program Design Including Data Structures

Java Programming: Program Design Including Data Structures2 Chapter Objectives  Learn about binary trees  Explore various binary tree traversal algorithms  Learn how to organize data in a binary search tree  Discover how to insert and delete items in a binary search tree

Java Programming: Program Design Including Data Structures3 Binary Trees  A binary tree, T, is either empty or  T has a special node called the root node  T has two sets of nodes, L T and R T, called the left subtree and right subtree  L T and R T are binary trees  A binary tree can be shown pictorially

Java Programming: Program Design Including Data Structures4 Binary Trees (continued) Figure 19-1 Binary tree

Java Programming: Program Design Including Data Structures5 Binary Trees (continued) Figure 19-6 Various binary trees with three nodes

Java Programming: Program Design Including Data Structures6 Binary Trees (continued)  You can write a class that represents each node in a binary tree  Called BinaryTreeNode  Instance variables of the class BinaryTreeNode  info: stores the information part of the node  lLink: points to the root node of the left subtree  rLink: points to the root node of the right subtree

Java Programming: Program Design Including Data Structures7 Binary Trees (continued) Figure 19-7 UML class diagram of the class BinaryTreeNode and the outer-inner class relationship

Java Programming: Program Design Including Data Structures8 Binary Trees (continued) Figure 19-8 Binary tree

Java Programming: Program Design Including Data Structures9 Binary Trees (continued)  A leaf is a node in a tree with no children  Let U and V be two nodes in a binary tree  U is called the parent of V if there is a branch from U to V  A path from a node X to a node Y is a sequence of nodes X 0, X 1,..., X n such that:  X = X 0,X n = Y  X i-1 is the parent of X i for all i = 1, 2,..., n

Java Programming: Program Design Including Data Structures10 Binary Trees (continued)  Length of a path  The number of branches on that path  Level of a node  The number of branches on the path from the root to the node  Height of a binary tree  The number of nodes on the longest path from the root to a leaf

Java Programming: Program Design Including Data Structures11 Binary Trees (continued)  Method height private int height(BinaryTreeNode p) { if (p == null) return 0; else return 1 + Math.max(height(p.lLink), height(p.rLink)); }

Java Programming: Program Design Including Data Structures12 Copy Tree  Method copyTree private BinaryTreeNode copyTree (BinaryTreeNode otherTreeRoot) { BinaryTreeNode temp; if (otherTreeRoot == null) temp = null; else { temp = (BinaryTreeNode ) otherTreeRoot.clone(); temp.lLink = copyTree(otherTreeRoot.lLink); temp.rLink = copyTree(otherTreeRoot.rLink); } return temp; }//end copyTree

Java Programming: Program Design Including Data Structures13 Binary Tree Traversal  Item insertion, deletion, and lookup operations require that the binary tree be traversed  Commonly used traversals  Inorder traversal  Preorder traversal  Postorder traversal

Java Programming: Program Design Including Data Structures14 Inorder Traversal  Binary tree is traversed as follows:  Traverse left subtree  Visit node  Traverse right subtree

Java Programming: Program Design Including Data Structures15 Inorder Traversal (continued)  Method inOrder private void inorder(BinaryTreeNode p) { if (p != null) { inorder(p.lLink); System.out.print(p + “ “); inorder(p.rLink); }

Java Programming: Program Design Including Data Structures16 Preorder Traversal  Binary tree is traversed as follows:  Visit node  Traverse left subtree  Traverse right subtree

Java Programming: Program Design Including Data Structures17 Preorder Traversal (continued)  Method preOrder private void preorder(BinaryTreeNode p) { if (p != null) { System.out.print(p + “ “); preorder(p.lLink); preorder(p.rLink); }

Java Programming: Program Design Including Data Structures18 Postorder Traversal  Binary tree is traversed as follows:  Traverse left subtree  Traverse right subtree  Visit node

Java Programming: Program Design Including Data Structures19 Postorder Traversal (continued)  Method postOrder private void postorder(BinaryTreeNode p) { if (p != null) { postorder(p.lLink); postorder(p.rLink); System.out.print(p + “ “); }

Java Programming: Program Design Including Data Structures20 Implementing Binary Trees Figure UML class diagram of the interface BinaryTreeADT

Java Programming: Program Design Including Data Structures21 Implementing Binary Trees (continued) Figure UML class diagram of the class BinaryTree

Java Programming: Program Design Including Data Structures22 Implementing Binary Trees (continued)  Method clone public Object clone() { BinaryTree copy = null; try { copy = (BinaryTree ) super.clone(); } catch (CloneNotSupportedException e) { return null; } if (root != null) copy.root = copyTree(root); return copy; }

Java Programming: Program Design Including Data Structures23 Binary Search Trees  To search for an item in a normal binary tree, you must traverse entire tree until item is found  Search process will be very slow  Similar to searching in an arbitrary linked list  Binary search tree  Data in each node is  Larger than the data in its left child  Smaller than the data in its right child

Java Programming: Program Design Including Data Structures24 Binary Search Trees (continued) Figure Binary search tree

Java Programming: Program Design Including Data Structures25 Binary Search Trees (continued) Figure UML class diagram of the class BinarySearchTree and the inheritance hierarchy

Java Programming: Program Design Including Data Structures26 Search  Searches tree for a given item  General steps  Compare item with info in root node  If they are the same, stop the search  If item is smaller than info in root node  Follow link to left subtree  Otherwise  Follow link to right subtree

Java Programming: Program Design Including Data Structures27 Insert  Inserts a new item into a binary search tree  General steps  Search tree and find the place where new item is to be inserted  Search algorithm is similar to method search  Insert new item  Duplicate items are not allowed

Java Programming: Program Design Including Data Structures28 Delete  Deletes item from a binary search tree  After deleting items, resulting tree must be a binary search tree  General steps  Search the tree for the item to be deleted  Searching algorithm is similar to method search  Delete item

Java Programming: Program Design Including Data Structures29 Delete (continued)  Delete operation has four cases  Case 1: Node to be deleted is a leaf  Case 2: Node to be deleted has no left subtree  Case 3: Node to be deleted has no right subtree  Case 4: Node to be deleted has nonempty left and right subtrees  search left subtree of the node to be deleted to find its immediate predecessor

Java Programming: Program Design Including Data Structures30 Binary Search Tree: Analysis  Performance depends on shape of the tree  If tree shape is linear, performance is the same as for a linked list  Average number of nodes visited 1.39log 2 n = O(log 2 n)  Average number of key comparisons 2.77log 2 n = O(log 2 n)

Java Programming: Program Design Including Data Structures31 Nonrecursive Binary Tree Traversal Algorithms  Traversal algorithms  Inorder  Preorder  Postorder

Java Programming: Program Design Including Data Structures32 Nonrecursive Inorder Traversal  Method nonRecursiveInTraversal public void nonRecursiveInTraversal() { LinkedStackClass > stack = new LinkedStackClass >(); BinaryTreeNode current; current = root; while ((current != null) || (!stack.isEmptyStack())) if (current != null) { stack.push(current); current = current.lLink; }

Java Programming: Program Design Including Data Structures33 Nonrecursive Inorder Traversal (continued) else { current = (BinaryTreeNode ) stack.peek(); stack.pop(); System.out.print(current.info + “ “); current = current.rLink; } System.out.println(); }

Java Programming: Program Design Including Data Structures34 Nonrecursive Preorder Traversal  General algorithm create stack current = root; while (current is not null or stack is nonempty) if (current is not null) { visit current; push current onto stack; current = current.lLink; } else { pop stack into current; current = current.rLink; //prepare to visit right subtree }

Java Programming: Program Design Including Data Structures35 Nonrecursive Postorder Traversal  General algorithm  Mark left subtree of node as visited  Visit left subtree and return to node  Mark right subtree of node as visited  Visit right subtree and return to node  Visit node

Java Programming: Program Design Including Data Structures36 An Iterator to a Binary Tree  You can create an iterator for a binary tree  Iterator can traverse tree using  Inorder traversal  Preorder traversal  Postorder traversal

Java Programming: Program Design Including Data Structures37 AVL (Height-Balanced) Trees  Search performance depends on shape of the tree  You want the tree to be balanced  AVL (height-balanced) tree  Resulting binary search tree is nearly balanced  Perfectly balanced binary search tree  Heights of the left and right subtrees are equal  Left and right subtrees are perfectly balanced binary trees

Java Programming: Program Design Including Data Structures38 AVL (Height-Balanced) Trees(continued) Figure Perfectly balanced binary tree

Java Programming: Program Design Including Data Structures39 AVL (Height-Balanced) Trees (continued)  AVL tree: A binary search tree where  Heights of left and right subtrees differs by at most 1  Left and right subtrees are AVL trees  Balance factor  Difference between height of right subtree and height of left subtree

Java Programming: Program Design Including Data Structures40 AVL (Height-Balanced) Trees (continued) Figure Perfectly balanced binary tree

Java Programming: Program Design Including Data Structures41 Insertion into AVL Trees  General steps  Search AVL tree to find insertion point  Insert new item  Duplicate items are not allowed  Rebalance tree (if needed)

Java Programming: Program Design Including Data Structures42 Insertion into AVL Trees (continued) Figure AVL tree before inserting 90

Java Programming: Program Design Including Data Structures43 Insertion into AVL Trees (continued) Figure Binary search tree of Figure after inserting 90 ; nodes other than 90 show their balance factors before insertion

Java Programming: Program Design Including Data Structures44 Insertion into AVL Trees (continued) Figure AVL tree of Figure after inserting 90 and adjusting the balance factors

Java Programming: Program Design Including Data Structures45 AVL Tree Rotations  Reconstruction procedure  Types of rotations  Left rotation  Nodes from right subtree move to left subtree  Root of right subtree becomes root of reconstructed subtree  Right rotation  Nodes from left subtree move to right subtree  Root of left subtree becomes root of reconstructed subtree

Java Programming: Program Design Including Data Structures46 AVL Tree Rotations (continued) Figure Left rotation at a

Java Programming: Program Design Including Data Structures47 AVL Tree Rotations (continued) Figure Right rotation at b

Java Programming: Program Design Including Data Structures48 AVL Tree Rotations (continued)  Method rotateToLeft private AVLNode rotateToLeft(AVLNode root) { AVLNode p; //reference variable to the root of the right subtree of root if (root == null) System.err.println(“Error in the tree.”); else if (root.rLink == null) System.err.println(“Error in the tree: “ + “No right subtree to rotate.”); else { p = root.rLink; root.rLink = p.lLink; //the left subtree of p becomes the right //subtree of root p.lLink = root; root = p; //make p the new root node } return root; }//end rotateToLeft

Java Programming: Program Design Including Data Structures49 AVL Tree Rotations (continued)  Method rotateToRight private AVLNode rotateToRight(AVLNode root) { AVLNode p; //reference variable to the root of the //left subtree of root if (root == null) System.err.println(“Error in the tree.”); else if (root.lLink == null) System.err.println(“Error in the tree: “ + “No left subtree to rotate.”); else { p = root.lLink; root.lLink = p.rLink; //the right subtree of p //becomes the left subtree of root p.rLink = root; root = p; //make p the new root node } return root; }//end rotateToRight

Java Programming: Program Design Including Data Structures50 AVL Tree Rotations (continued) Figure AVL tree after inserting 40 Figure AVL tree after inserting 30

Java Programming: Program Design Including Data Structures51 AVL Tree Rotations (continued) Figure AVL tree after inserting 20

Java Programming: Program Design Including Data Structures52 AVL Tree Rotations (continued) Figure AVL tree after inserting 25

Java Programming: Program Design Including Data Structures53 Deletion from AVL Trees  General steps  Find node to be deleted  Delete node  Four cases arise:  Node to be deleted is a leaf  Node to be deleted has no right child  Node to be deleted has no left child  Node to be deleted has both children

Java Programming: Program Design Including Data Structures54  Height of AVL tree with n nodes (worst case) 1.44log 2 n = O(log 2 n)  Time to manipulate an AVL tree in the worst case is no more than 44% of optimum time  Average search time of an AVL tree is about 4% more than the optimum Analysis: AVL Trees

Java Programming: Program Design Including Data Structures55 Programming Example: Video Store (Revisited)  Program in Chapter 16 used a linked list to keep track of video inventory  Search could be time consuming  Modify program to use a binary tree instead  Insertion and deletion in a binary search tree is faster than in a linked list

Java Programming: Program Design Including Data Structures56 Chapter Summary  Binary trees  Every node has only two children  Left subtree  Right subtree  Binary tree traversal  Inorder  Preorder  Postorder

Java Programming: Program Design Including Data Structures57 Chapter Summary (continued)  Binary search trees  Each node is greater than elements in its left subtree and less than elements in its right subtree  AVL (height-balanced) trees  Binary search tree  Heights of left and right subtrees differs by at most 1  Left and right subtrees of the root node are AVL trees