This document is a lecture slide presentation for CSE110 Principles of Programming with Java at Arizona State University. It reviews exam questions and covers searching algorithms like linear search and binary search. Linear search sequentially checks each element to find a target. Binary search uses divide and conquer to eliminate half the search space with each comparison by checking the middle element. Pseudocode is provided to implement both search algorithms.

1. CSE110
Principles of Programming
with Java
Lecture 27:
Exam review and Searching Algorithms
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

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Q17

8. Searching

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Search Algorithms
• Search: locate an item in an array of information
(primitive type or objects)
• Common searching algorithms includes:
• Linear search
• Binary search

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Linear Search
• Looks sequentially at each element of a given
collection of elements until either the target is found
or we come to the end of the list (not found)

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Linear Search
// Searches and returns the index of where the
// searched element is located.
// Returns -1 if the target is not found.
public static int linearSearch (int[] numbers, int target) {
int position = -1; //it is not found yet
for (int index=0; index < numbers.length; index++) {
if (numbers[index] == target) {
position = index; //save the index of search element
break;
// OR
// return index;
}
}
return position;
}

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Binary Search
• Binary Search is used to look up a word in a dictionary or
a name in a phone book.
• It uses Divide and Conquer approach.
• Pre-Condition of Binary Search: The search pool is sorted.
• A binary search eliminates large parts of the search pool
with each comparison
• Instead of starting the search at one end, we begin in
the middle
• If the target isn't found, we know that if it is in the pool at
all, it is in one half or the other
• We can then jump to the middle of that half, and
continue similarly

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Binary Search
• For example, find the number 29 in the following sorted list of
numbers:
• Compare the target to the middle value 54
• We now know that if 29 is in the list, it is in the front half of the list
since it is smaller than 54.
• With one comparison, we’ve eliminated half of the data
• Then compare to 22, eliminating another quarter of the data,
etc.
8 15 22 29 36 54 55 61 70 73 88

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Binary Search
// Searches using a binary search
// returns the index of where the searched element is located.
// Returns -1 if the target is not found.
public static int binarySearch (int[] data, int target) {
int start = 0, end = data.length-1, middle;
int position = -1; //return -1 if not found
boolean found = false;
while (found == false && start <= end) {
middle = (start+end)/2;
if (data[middle] == target){
found = true;
position = middle;
} else if (data[middle] > target)
end = middle - 1;
else
start = middle + 1;
}
return position; //return -1 if not found
}

15. CSE110 - Principles of Programming
Javier Gonzalez-Sanchez
javiergs@asu.edu
Summer 2017
Disclaimer. These slides can only be used as study material for the class CSE110 at ASU. They cannot be distributed or used for another purpose.