Array Review Selection Sort

Get out your notes. Array ReviewSelection Sort

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.

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 ] + " " );

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 ] + " " );

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 ] + " " );

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 ] + " " )

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 );

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 );

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 );

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++ ) { _______________________ }

Dry Run 8 int [] list = { 10, 11, 4, 8, 2 } ; for(intstart = 1; start < list.length; start++) { inttemp = 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();

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) }

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.

What did the previous Code do?

How it works Example Low High 2 6 8 3 15 1 7 Stability Speed Your turn High Low 8 2 5 3 9 4 6 1 7 Check, mark, switch Not stable O(n2) Selection sort

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)

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.

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.

Array Review Selection Sort