Sorting

1
Sorting

• Summary of Sorting Algorithms

2
_Plan

• General idea of sorting we start with an array
  of items in no particular order, and we want to
  convert it into a sorted array in either
  ascending or descending order.

3
Definition Selection Sort (array of double
numbers)

• Find the smallest element in the entire array A
  and swap it with the first element--now the first
  element is in the correct position
• Find the smallest element in A minus the first
  element, and swap it with the second element--now
  the first two elements are in the correct order.
• Find the smallest element in A disregarding the
  first two elements, and swap it with the third
  element. Now the first three elements are in the
  correct order. Continue in this fashion.
• This algorithm is illustrated by the following
  figure
• Figure How Selection Sort works
• public static boolean search(double A, double
  key)
• for (int i 0 i lt A.length i)
• if (Ai key)
• return true
• return false

4
Example (Selection)
5
Search which returns the object esired
3

• 22 is the smallest overall number and is swapped
  with the first number
• 27 is the smallest number starting at the second
  one, and swapped with itself
• 45 is the smallest number starting at the third,
  and swapped with the third

6
Definition Bubble Sort (Exchange Sort)

• Process the full array by comparing consecutive
  elements if the (i1)st element is less than the
  ith element, swap them with each other, otherwise
  leave them alone.
• If no exchange is made, the array is sorted and
  we are done.
• At the end of this pass the overall largest
  number will have "bubbled" to the last position
  of the array.
• Repeat this "bubbling" procedure, but apply it to
  the current array except the last element.

7
Definition Bubble Sort (Exchange Sort)

• If no exchange was made, the array is sorted and
  we are done. At the end of this pass the
  second-largest number will have "bubbled" to the
  second-last position of the array.
• Repeat this "bubbling" procedure, but apply it to
  the current array except the last two elements.
  If no exchange was made, the array is sorted and
  we are done.
• Continue in this fashion until either no exchange
  was necessary during a particular pass, or there
  is nothing left to sort.

8
Example (Bubble)
9
Definition Insertion Sort

• Consider the second last element in the array. If
  the last element is less than this one, move it
  up by one and insert the second-last element in
  the last position.
• Consider the third-last element in the array, and
  the last two elements of the array. Move all
  entries in that subarray that are less than the
  third-last element up by one, and insert the
  third-last element into the resulting empty slot.

10
Example (Insertion)
11
Implementation

• if (userArrayn lt userArraycounter)
• // Swap the numbers in the array
• temp userArrayn
• userArrayn userArraycounter
• userArraycounter temp

12
Demonstrate

• Goto SelectBinary.java
• http//sciris.shu.edu/thinklets--------go to
  COmpSci---------Sorting

13
Code

• /
• Author(s) Felicia Escorpizo, Chunkai Szu,
  Rehan Malik
• Date June 13, 2000
• Program SelectBinary.java
• Description Get and sort array according to
  selection sort algorithm and perform binary
  search
• Pre-condition/Post-Condition Get the values
  from the user to input into the array.
• Print the original array and sorted
  array.
• Print the value in the array to search
  for (if selectec).
• Design Roles Initialize array and fill
  with values
• Initialize a few counter int values
• Design Idea
• 1. Get the array from the user and input into
  an array.
• 2. Print the original array.
• 3. Run selection sort algorithm
• a. Select first value and compare against the
  rest of the values. (switch if need)