searching chapter 16 slides by steve armstrong letourneau university longview, tx 2007, prentice...

Searching

Chapter 16

Slides by Steve ArmstrongLeTourneau University

Longview, TX2007,Prentice Hall

Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X

Chapter Contents• The Problem• Searching an Unsorted Array

Iterative Sequential Search Recursive Sequential Search Efficiency of Sequential Search

• Searching a Sorted Array Sequential search Binary Search Java Class Library: the Method binarySearch

Efficiency of Binary Search


Chapter Contents• Searching an Unsorted Chain

Iterative Sequential Search Recursive Sequential Search Efficiency of Sequential Search of a Chain

• Searching a Sorted Chain Sequential Search Binary Search

• Choosing a Search Method


The Problem

Fig. 16-1 Searching is an every day occurrence.


Searching an Unsorted Array

• An iterative search of an unsorted array

public boolean contains (T anEntry){ boolean found = false; for (int index = 0; !found && (index < length); index++) { if (anEntry.equals (list [index])) found = true ; } // end for return found;} // end contains

public boolean contains (T anEntry){ boolean found = false; for (int index = 0; !found && (index < length); index++) { if (anEntry.equals (list [index])) found = true ; } // end for return found;} // end contains



Fig. 16-2 An iterative sequential search of an

array that (a) finds its target



Fig. 16-2 An iterative sequential search of an array that (b) does not find its target


Recursive Sequential Search an Unsorted Array

• Pseudocode for a recursive algorithm to search an array.

• View source code of Java implementation


Recursive Sequential Search an Unsorted Array

Fig. 16-3 A recursive sequential search of an array that (a) finds its target; (b) does not find its target.


Efficiency of a Sequential Search

• Best case O(1) Locate desired item first

• Worst case O(n) Must look at all the items

• Average case O(n) Must look at half the items O(n/2) is still O(n)


Searching a Sorted Array

• A sequential search can be more efficient if the data is sorted

Fig. 16-4 Coins sorted by their mint dates.


Binary Search of Sorted Array

Fig. 16-5 Ignoring one-half of the data when the data is sorted.



• View algorithm for a search a[0] through a[n-1]

• View algorithm for binary search of a range of an array

• Note version which checks for existence of the desired item



Fig. 16-6 A recursive binary search of a

sorted array that (a) finds its target;



Fig. 16-6 A recursive binary

search of a sorted array that (b) does not find its target.

Click to view Java version of method binarySearch in

context

Click to view Java version of method binarySearch in

context


Java Class Library: The Method binarySearch

• The class Arrays in java.util defines versions of a static method with following specification:


Efficiency of a Binary Search


• Worst case O(log n) Must look at all the items

• Average case O(log n)


Iterative Sequential Search of an Unsorted Chain

Fig. 16-7 A chain of linked nodes that contain the entries in a list.


Sequential Search of an Unsorted Chain

• View implementation of iterative sequential search

• View recursive version of sequential search Note method contains which calls it


Efficiency of a Sequential Search of a Chain


• Worst case O(n) Must look at all the items

• Average case O(n) Must look at half the items O(n/2) is just O(n)


Searching a Sorted Chain

• Method to search a sorted chain

Note: Binary search of a chain of linked nodes is impractical.

Note: Binary search of a chain of linked nodes is impractical.


Choosing a Search Method

Fig. 16-8 The time efficiency of searching, expressed in Big Oh notation

searching chapter 16 slides by steve armstrong letourneau university longview, tx 2007, prentice...

Documents

iterative search

x recursive sequential

search method

data structures

pearson education

sequential search best

target slide

unsorted array pseudocode