abstract containers

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abstract containers

hierarchical (1 to many)

graph (many to many)first ith last

sequence/linear (1 to 1)

set

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treeshierarchical organization

each item has 1 predecessor and 0 or more successors

one item (root) has 0 predecessorsgeneral tree - no limit on number of

successorsbinary tree - 2 successors (left and

right)binary search tree is one use of a

binary tree data structure (will deal with later)

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tree terminologyThere is a uniquepath from the rootto each node.

Root is a level 0, childis at level(parent) + 1.

Depth/height of a treeis the length of the longest path.

level 0

1

2

3

4

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trees are recursive

Each node is the rootof a subtree.

Many tree processingalgorithms are bestwritten recursively.

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binary tree Each node has two successors

one called the left child one called the right child left child and/or right child may be empty

A binary tree is either - empty or - consists of a root and two binary trees, one called the left subtree and one called the right subtree

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binary tree density (shape) a binary tree of depth n is complete iff

levels 1 .. n have all possible nodes filled-in level 1: 1 level 2: 2 level 3: 4 level n: ?

nodes at level n occupy the leftmost positions max nodes level at n: 2n-1

max nodes in binary tree of depth n: 2n-1 depth of binary tree with k nodes: >floor[log2

k] depth of binary tree with k nodes: <ceil[log2

k] longest path is O(log2 k)

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representing a binary tree

have to store items and relationships (predecessor and successors information)

array representation each item has a position number (0 .. n-1) use the position number as an array index

O(1) access to parent and children of item at position i wastes space unless binary tree is complete

linked representation each item stored in a node which contains:

the item a pointer to the left subtree a pointer to the right subtree

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array representation each item has a position number

root is at position 0 root's left child is at position 1 root's right child is at position 2

in general: left child of i is at 2i + 1 right child of i is at 2i + 2 parent of i is at (i-1)/2

0 1 2

3 4 5 6

0 1 2 3 4 5 6 - - - - - - -

0 1 2

6

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works well if n is known in advance and there are no "missing" nodes

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linked representation

class binTreeNode {public: T item; binTreeNode * left; binTreeNode * right; binTreeNode (const T & value) { item = value; left = NULL; right = NULL; }};binTreeNode * root;

root

left child of *p?right child of *p?parent of *p?

p

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why is a binary tree so useful?

for storing a collection of values that has a binary hierarchical organization arithmetic expressions boolean logic expressions Morse or Huffman code trees

data structure for a binary search tree

general tree can be stored using a binary tree data structure

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an expression tree an arithmetic

expression consists of an operator and two operands (either of which may be an arithmetic expression)

some simplifications only binary operators

(+, *, /, -) only single digit, non-

negative integer operands

*- +

5 2 6 1

operands are stored in leaf nodesoperators are stored in branch nodes

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traversing a binary tree

what does it mean to traverse a container? "visit" each item once in some order

many operations on a collection of items involve traversing the container in which they are stored displaying all items making a copy of a container

linear collections (usually) traversed from first to last last to first is an alternative traversal order

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binary tree traversalsorder in which to "visit" the items?some common orders - visit an

item before its children (preorder) after its children (postorder) between its children (inorder) level by level (level order)

by convention go left before right

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traversing an expression tree

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*

+ *

1 3 - 2

1

preorder (1st touch) * + 1 3 * - 4 1 2

inorder (2nd touch) 1 + 3 * 4 - 1 * 2

postorder (last touch) 1 3 + 4 1 - 2 * *

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expression tree traversal

traverse (ExprTree) { if (root of ExprTree holds a digit) //is a leaf node visit (root); else // root holds an operand { visit (root) traverse (ExprTree's left subtree) traverse (ExprTree's right subtree) }}

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expression tree operations

use "recursive partners" allow recursive calls to deal with a subtree

(identifed by a pointer to its root node) build uses a preorder traversal copy uses a preorder traversal postfix uses a postorder traversal clear uses a postorder traversal what kind of traversal does infix need? what kind of traversal does evaluate

need?

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Associative Containersfast searching

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STL Containers

Sequence containers vector list deque

Adapters stack queue priority_queue

Associative containers set map multiset multimap

unique keys non unique keys keys only set multiset

key, value pairs map multimap

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map containers allow storing a collection of items each of

which has a key which uniquely identifies it student records (social security number) books in a library (ISBN) identifiers appearing in a function (name)

has operations to insert an item (key-value pair) delete the item with a given key retrieve the item with a given key

operations based on value, not position searching for a key is the critical operation

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some possible data structures

array (or STL vector) unordered ordered by keys

linked list (or STL list) unordered ordered by keys

binary search tree balanced search trees hash table

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comparative performance

data structure Retrieve Insert Delete

unordered array

ordered array

unordered linked list

ordered linked list

O(n) O(1) O(n)

O(log2n) O(n) O(n)

O(n) O(1) O(n)

O(n) O(n) O(n) search trees and hash table both have better performance

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binary search tree

each item is stored in a node of a binary tree

each node is the root of a binary tree with the BST property all items stored in its left subtree have

smaller key values all items stored in its right subtree have

larger key values May be lop-sided. Insertion order

matters.

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the BSTree<TE, KF> class

BSTreeNode has same structure as binary tree nodes

elements stored in a BSTree are a key-value pair must be a class (or a struct) which has

a data member for the value a data member for the key a method with the signature: KT key( )

const; where KT is the type of the key

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an examplestruct treeItem{ int id; // key string data; // value int key( ) const { return id; }};BSTree<treeItem, int> myBSTree;

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a binary search tree

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root

This is NOT a Heap!!

No node

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traversing a binary search tree

can use any of the binary tree traversal orders – preorder, inorder, postorder base case is reaching an empty tree

inorder traversal visits the elements in order of their key values

how would you visit the elements in descending order of key values?

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Recursive BST Search Algorithm

void search (bstree, searchKey){ if (bstree is empty)

//base case: item not found. Take needed action else if (key in bstree's root == search Key) // base case: item found. Process it.

else if (searchKey < key in bstree's root ) search (leftSubtree, searchKey); else search (rightSubtree, searchKey);}

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searching for 40

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root

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searching for 30

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root

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Recursive BST InsertionSimilar to BST search:Insert_aux (nodeptr & subtree, &item)

If (subtree.root.empty( ) ) subtree.root=itemElse if (item < subtree.root)

Insert_aux (subtree.left, item) // try insert on left

Else if (item > subtree.root)Insert_aux (subtree.left, item) // try insert on

right Else already in tree

Just keep moving down the tree

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deletion cases item to be deleted is in a leaf node

pointer to its node (in parent) must be changed to NULL

item to be deleted is in a node with one empty subtree pointer to its node (in parent) must be

changed to the non-empty subtree item to be deleted is in a node with

two non-empty subtrees

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the easy cases36

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21 40

Just prune it

Just set its parent (42) to skip this node

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the “hard” case36

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21 40

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the “hard” case

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replace with smallest in right subtree (its inorder successor)

replace with largest in left subtree (its inorder predecessor)

or

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Using method 1

Replace with in-order predecessor

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Method 2

Replace with in-order successor

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big O of BST operations

measured by length of the search path depends on the height of the BST height determined by order of

insertionheight of a BST containing n items

is minimum: floor (log2 n) maximum: n - 1 average: ?

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faster searching"balanced" search trees guarantee

O(log2 n) search path by controlling height of the search tree AVL tree 2-3-4 tree red-black tree (used by STL associative

container classes)hash table allows for O(1) search

performance search time does not increase as n

increases