1. Array Review Selection Sort Get out your notes.

2. Learning Objectives Be able to dry run programs that use arrays Be able to dry run programs that use arrays. Understand and be able to implement a Selection Sort.

3. Dry run 1 int[] egArray = { 2, 4, 6, 8, 10, 1, 3, 5, 7, 9 }; for ( int index= 0 ; index < 5 ; index++ ) System.out.print( egArray[ index ] + " " );

4. Dry Run 2 int[] egArray = { 2, 4, 6, 8, 10, 1, 3, 5, 7, 9 }; for ( int index= 0 ; index < egArray.length ; index++ ) System.out.print( egArray[ index ] + " " );

5. Dry Run 3 int[] egArray = { 2, 4, 6, 8, 10, 1, 3, 5, 7, 9 }; for ( int index= 0 ; index < egArray.length ; index = index + 2 ) System.out.print( egArray[ index ] + " " );

6. Modify the code Fill in the blanks of the following code fragment so that the elements of the array are printed in reverse order, starting with the last element. int[] egArray = { 2, 4, 6, 8, 10, 1, 3, 5, 7, 9 }; for ( int index= ________ ; _____________ ; ______________ ) System.out.print( egArray[ index ] + " " )

7. Dry Run 4 int[] array = { 1, 4, 3, 6, 8, 2, 5}; int what = array[0]; // scan the array for ( int index=0; index < array.length; index++ ) { if ( array[ index ] > what ) what = array[ index ]; } System.out.println( what );

8. Dry Run 5 int[] array = { 1, 4, 3, 6, 8, 2, 5}; int what = array[0]; // scan the array for ( int index=0; index < array.length; index++ ) { if ( array[ index ] < what ) what = array[ index ]; } System.out.println( what );

9. Dry Run 6 int[] array = { 1, 4, 3, 6 }; int what = 0; // scan the array for ( int index=0; index < array.length; index++ ) { what = what + array[ index ] ; } System.out.println( what );

10. 7) Fill in the blank in the following code fragment so that each element of the array is assigned twice the value of its index. int[] array = new int[10]; // scan the array for ( int index=0; index < array.length; index++ ) { _______________________ }

11. Dry Run 8 int [] list = { 10, 11, 4, 8, 2 } ; for(int start = 1; start < list.length; start++) { int temp = list[start]; int k = start; while(k > 0 && list[k-1] > temp) { list[k] = list[k-1]; k--; } list[k] = temp; } for (int s:list) System.out.print(s +" "); System.out.println();

12. Dry Run 9 public static void main (String [] args) { int [] a = { 10, 11, 4, 8, 2 } ; int out, in, min; int dummy; for (out=0; out<a.length-1; out++) { min = out; for(in=out+1; in<a.length; in++) if(a[in] < a[min] ) min = in; dummy = a[out]; a[out] = a[min]; a[min] = dummy; for (int s:a) System.out.print(s +" "); System.out.println(); } // end for(out) }

13. Learning Objectives Review reading a nested loop program. Understand how the selection and insertion sorts work Write a program that uses the selection and insertion sorts.

14. What did the previous Code do?

15. Selection sort How it works Example LowHigh 2 6 8 3 15 1 7 Stability Speed Your turn HighLow 8 2 5 3 9 4 6 1 7 Check, mark, switch Not stable O(n 2 )

16. Selection Sort //a is the array name, // nElems = the number of elements being sorted int out, in, min; int dummy; // If sorting an array of ints for(out=0; out<nElems-1; out++) // outer loop { min = out; // minimum for(in=out+1; in<nElems; in++) // inner loop if(a[in] < a[min] ) // Check if min greater, min = in; // Mark, we have a new min dummy = a[out]; //Switch a[out] = a[min]; a[min] = dummy; } // end for(out)

17. First Program Check for Understanding import java.util.Scanner; // program uses class Scanner public class SelectionSort { public static void main(String args[]) { String[] names = new String[5]; String name; // create Scanner to obtain input from command window Scanner input = new Scanner( System.in ); for (int count = 0 ; count < names.length; count++) { System.out.println("Please enter a name"); names[count] = input.next(); } for (int j=0; j<names.length; j++) { System.out.println(names[j]); } //Insert Sort Code here System.out.println("The names..."); for (String temp: names) // For each String temp in the array names. System.out.println(temp); } } Enter this into BlueJ and test to make sure it is sorting.

18. Selection Sort Program Input 11 scores Output: –Numbers in sorted order (Low to High) –Mean (average) –Median (Middle number after sorting) Push: –Find the mode –Let the user tell you how many scores prior to entering the scores –Modify it so the user can continually enter scores (semantics of a while loop) and calculates the above when they are finished.