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Java - Reverse Selection Sort

Anonymous User201905-Oct-2013

I am trying to create a program that does a selection sort but backwards. As in, finding the largest number and swapping it with the last. I have no idea why this isn't working.

UPDATED CODE according to comments.

  import java.util.Scanner;

public class Problem20 {

    public static void main(String[] args){ 
        int data[] = new int[10]; 
        Scanner scan = new Scanner(System.in); 
        System.out.print("Please enter 10 numbers: "); 
        for (int i = 0; i < 10; i++) 
        { 
        data[i] = scan.nextInt(); 
        } 
        sortBig(data); 
    } 
    public static void sortBig(int[] data){ 
        int i, j, maxIndex, tmp; 
          for (i = data.length - 1; i >= 0; i--) 
          { 
                maxIndex = i; 
                for (j = i-1; j >=0; j--) 
                    if (data[j] > data[maxIndex]) 
                      maxIndex = j; 
                    if (maxIndex != i) 
                    { 
                      tmp = data[data.length - 1]; 
                      data[data.length - 1] = data[maxIndex]; 
                      data[maxIndex] = tmp; 
                    } 
          } 
        for (int r = 0; r < data.length; r++){ 
            System.out.print(data[r] + " "); 
        } 
    } 
}
javajava 
Updated on 05-Oct-2013
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1 Answers

Anonymous User

Anonymous User

05-Oct-2013

Here is a simple test I wrote to find and make it easy to debug the code.

import org.junit.Test; 
import java.util.Arrays; 
import static org.junit.Assert.assertEquals; 
import static org.junit.Assert.assertTrue; 
public class Problem20 { 
    @Test 
    public void testSorting() { 
        // passes 
        assertTrue(Arrays.equals(new int[]{1, 2, 3}, sortBig(3, 2, 1))); 
        // failed previously 
        assertTrue(Arrays.equals(new int[]{1, 2, 3, 4}, sortBig(4, 3, 2, 1))); 
        // create an array of unique values in pseudo random order 
        int[] largeArray = new int[1000]; 
        for (int i = 0; i < largeArray.length; i++) 
            largeArray[i] = (i * 29) % largeArray.length; 
        int[] sortedArray = sortBig(largeArray); 
        for (int i = 0; i < largeArray.length; i++) 
            assertEquals(i, sortedArray[i]); 
    } 
    public static int[] sortBig(int... data) { 
        for (int i = data.length - 1; i >= 0; i--) { 
            int maxIndex = i; 
            for (int j = i - 1; j >= 0; j--) 
                if (data[j] > data[maxIndex]) 
                    maxIndex = j; 
            if (maxIndex != i) { 
// int tmp = data[data.length - 1]; 
                int tmp = data[i]; 
// data[data.length - 1] = data[maxIndex]; 
                data[i] = data[maxIndex]; 
                data[maxIndex] = tmp; 
            } 
        } 
        return data; 
    } 
}

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