This document discusses searching and sorting algorithms covered in CSE110 Principles of Programming with Java taught by Javier Gonzalez-Sanchez during Summer 2017. It covers linear search, binary search, and bubble sort. Binary search requires a pre-sorted list and divides the search space in half at each step. Bubble sort iterates through a list and swaps adjacent elements that are out of order until the list is fully sorted.

1. CSE110
Principles of Programming
with Java
Lecture 28:
Searching and Sorting
Javier Gonzalez-Sanchez
javiergs@asu.edu
javiergs.engineering.asu.edu
Office Hours: By appointment

2. Searching

3. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 3
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)

4. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 4
Binary Search
• It uses Divide and Conquer approach.
• Pre-Condition: The search pool is sorted.
• Instead of starting the search at one end, we begin
in the middle
• Used to look up a word in a dictionary or a name in
a phone book.

5. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 5
Binary Search
8 15 22 29 36 54 55 61 70 73 88
0 1 2 3 4 5 6 7 8 9 10
start, end, middle
0, 10, 5
0, 4, 2
3, 4, 3
3

6. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 6
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.

7. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 7
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
}

8. Sorting

9. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 9
Sorting
Sort: arrange values into an order such as
Alphabetical, Ascending numeric, or Descending
numeric
Two algorithms considered here :
• Bubble sort
• Selection sort

10. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 10
Bubble sort

11. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 11
Bubble sort

12. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 12
Bubble sort

13. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 13
Bubble sort
public static void bubbleSort(int[] array1) {
boolean swap;
do {
swap = false;
for (int index=0;index<=array1.length-2;index++) {
// compare element at index and at index+1
if (array1[index] > array1[index+1]) {
//swap them if they are not in the order
int temp = array1[index+1];
array1[index+1] = array1[index];
array1[index] = temp;
swap = true
}
}
} while (swap == true);
}

14. 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.