Lecture 5 tree.pptx

BINARY TREES
 A binary tree is a data structure which is defined as a collection of
elements called nodes. Every node contains a "left" pointer, a "right"
pointer, and a data element. Every binary tree has a root element pointed
by a "root" pointer. The root element is the topmost node in the tree. If
root = NULL, then it means the tree is empty.
 If the root node R is not NULL, then the two trees T1 and T2 are called
the left and right subtrees of R. if T1 is non-empty, then T1 is said to be
the left successor of R. likewise, if T2 is non-empty then, it is called the
right successor of R.
8
1
32
4
5 6 7
1
2
1
0
1
1
ROOT NODE
T2T1
9
In a binary tree every node has 0, 1 or at the
most 2 successors. A node that has no
successors or 0 successors is called the leaf
node or the terminal node.

KEY TERMS
 Sibling: If N is any node in T that has left successor S1 and right successor
S2, then N is called the parent of S1 and S2. Correspondingly, S1 and S2
are called the left child and the right child of N. Also, S1 and S2 are said to
be siblings. Every node other than the root node has a parent. In other
words, all nodes that are at the same level and share the same parent are
called siblings (brothers).
Level number: Every node in the binary tree is assigned a level number.
The root node is defined to be at level 0. The left and right child of the root
node has a level number 1. Similarly, every node is at one level higher than
its parents. So all child nodes are defined to have level number as parent’s
level number + 1.
 Degree: Degree of a node is equal to the number of children that a node
has. The degree of a leaf node is zero.
In-degree of a node is the number of edges arriving at that node. The root
node is the only node that has an in-degree equal to zero. Similarly,
Out-degree of a node is the number of edges leaving that node.
Leaf node: A leaf node has no children.

KEY TERMS contd.
Similar binary trees: Given two binary trees T and T’ are said to be similar if both
of these trees have the same structure.
A
CB
D
E
F
HG
I
J
TREE T’
TREE T”
Copies of binary trees: Two binary trees T and T’ are said to be copies if they have
similar structure and same contents at the corresponding nodes.
A
CB
D E
A
CB
D
E
TREE T’
TREE T”

KEY TERMS contd.
 Directed edge: Line drawn from a node N to any of its successor is called a
directed edge. A binary tree of n nodes have exactly n – 1 edges (because, every
node except the root node is connected to its parent via an edge).
 Path: A sequence of consecutive edges is called a path.
 Depth: The depth of a node N is given as the length of the path from the root R to
the node N. The depth of the root node is zero. The height/depth of a tree is
defined as the length of the path from the root node to the deepest node in the
tree.
A tree with only a root node has a height of zero. A binary tree of height h, has at
least h nodes and at most 2h – 1
nodes. This is because every level will have at least
one node and can have at most 2 nodes. So, if every level has two nodes then a
tree with height h will have at the most 2h – 1
nodes as at level 0, there is only one
element called the root. The height of a binary tree with n nodes is at least n and
at most log2(n+1)
 Ancestor and descendant nodes: Ancestors of a node are all the nodes along the
path from the root to that node. Similarly, descendants of a node are all the nodes
along the path from that node to the leaf node.
 Binary trees are commonly used to implement binary search trees, expression
trees, tournament trees and binary heaps.

Complete Binary Trees
 A complete binary tree is a binary tree which satisfies two properties. First, in a
complete binary tree every level, except possibly the last, is completely filled.
Second, all nodes appear as far left as possible
 In a complete binary tree Tn, there are exactly n nodes and level r of T can have at
most 2r
nodes.
 The formula to find the parent, left child and right child can be given as- if K is a
parent node, then its left child can be calculated as 2 * K and its right child can be
calculated as 2 * K + 1. For example, the children of node 4 are 8 (2*4) and 9 (2* 4 +
1). Similarly, the parent of the node K can be calculated as | K/2 |. Given the node 4,
its parent can be calculated as | 4/2 | = 2. The height of a tree Tn having exactly n
nodes is given as,
 Hn = | log2 n + 1 |
 This means, if a tree T has 10,00,000 nodes then its height is 21.
1
32
4
8
5 6
7
1310 119 12

Representation of Binary Trees
in Memory
 In computer’s memory, a binary tree can be maintained either using
a linked representation (as in case of a linked list) or using
sequential representation (as in case of single arrays).
Linked Representation of Binary TreesLinked Representation of Binary Trees
 In linked representation of binary tree, every node will have three
parts, the data element, a pointer to the left node and a pointer to
the right node. So in C, the binary tree is built with a node type
given as below.
struct node {
struct node* left;
int data;
struct node* right;
};
1
2 3
4 5 6 7
X 8 X X 9 X X 10 X X 11 X X 12 X

Sequential Representation of
Binary Trees
 Sequential representation of trees is done using single or one
dimensional array. Though, it is the simplest technique for memory
representation but it is very inefficient as it requires a lot of memory
space. A sequential binary tree follows the rules given below:
 One dimensional array called TREE, will be used.
 The root of the tree will be stored in the first location. That is,
TREE[0] will store the data of the root element.
 The children of a node K, will be stored in location (2*K) and
(2*K+1).
 The maximum size of the array TREE is given as (2d+1
-1), where d is
the depth of the tree.
 An empty tree or sub-tree is specified using NULL. If TREE[0] =
NULL, then the tree is empty.
0 20
1 15
2 35
3 12
4 17
5 21
6 39
7
8
9 16
10 18
12
13
14 36
15 45
16
17
18
3515
12
17 2
1
39
45
1
6
18
3
6
20

EXPRESSION TREES
 Binary trees are widely used to store algebraic expressions. For
example, consider the algebraic expression Exp given as,
 Exp = (a – b ) + ( c * d)
 This expression can be represented using a binary tree as shown in
figure
+
*-
a b c d

TRAVERSING OF A BINARY TREE
 Traversing a binary tree is the process of visiting each node in the tree
exactly once, in a systematic way. Unlike linear data structures in which the
elements are traversed sequentially, tree is a non-linear data structure in
which the elements can be traversed in many different ways. There are
different algorithms for tree traversals. These algorithms differ in the order in
which the nodes are visited. In this section, we will read about these
algorithms.
 Pre-order algorithm
To traverse a non-empty binary tree in preorder, the following operations are
performed recursively at each node. The algorithm starts with the root node of
the tree and continues by,
 Visiting the root node.
 Traversing the left subtree.
 Traversing the right subtree.
A
CB
D E
F
IH
GA, B, D, C, E, F, G, H and I

In-order algorithm
To traverse a non-empty binary tree in in-order, the following operations
are performed recursively at each node. The algorithm starts with the
root node of the tree and continues by,
Post-order algorithm
To traverse a non-empty binary tree in post-order, the following operations
are performed recursively at each node. The algorithm starts with the
root node of the tree and continues by,
A
CB
D E
F
IH
G
B, D, A, E, H, G, I, F AND C.
D, B, H, I, G, F, E, C and A.

Lecture 5 tree.pptx

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Lecture 5 tree.pptx