Java Selection Sort Modification

Question

So I made this selection sort code, but I want it to increment one loop of the sort each time the function is called.

So I thought okay. Why not just remove the outer for loop and replace index with a static variable up top and increment it each time the function finishes its operations. But that just messed up the sort really badly. Can someone help?

Question: How do I go through the sort one step at a time each time the function is called?

I don't want it to sort the entire thing all at once

private static void selectionSort(int[] array) {
    for (int index = 0; index < array.length; index++) {
        int currentMin = array[index];
        int indexOfMin = index;

        for(int j = index+1; j < array.length; j++) {
            if(array[j] < currentMin) { 
                currentMin = array[j];
                indexOfMin = j;
            }
        }
        swap(array, index, indexOfMin);
    }
}

private static void swap(int[] a, int i, int j) {
    int temp = a[i];
    a[i] = a[j];
    a[j] = temp;
}

Saw your edits. Do you mean you wanna print out every step of the program like 312 -> 132 -> 123? — jianweichuah
– jianweichuah, Commented Dec 14, 2015 at 5:05
Basically I'm showing this sort visually with bars, and each time I click the button it will step through the sort and adjust the bars — flowinwind
– flowinwind, Commented Dec 14, 2015 at 5:06

jianweichuah · Accepted Answer · 2015-12-14 05:16:58Z

1

Why wouldn't global variable do the job? Do you wanna post your solution and we can take a look? Or you can also just pass the starting index to the function and call it with incremental index every time the button is pressed.

private static void selectionSort(int fromIndex, int[] array) {
    int currentMin = array[fromIndex];
    int indexOfMin = fromIndex;

    for(int j = fromIndex+1; j < array.length; j++) {
        if(array[j] < currentMin) {
            currentMin = array[j];
            indexOfMin = j;
        }
    }
    swap(array, fromIndex, indexOfMin);
}

private static void swap(int[] a, int i, int j) {
    int temp = a[i];
    a[i] = a[j];
    a[j] = temp;
}

Then in main, call it like this:

for (int fromIndex = 0; fromIndex < array.length; fromIndex++) {
    // Stop here and wait for button click.
    selectionSort(fromIndex, array);
}

answered Dec 14, 2015 at 5:16

jianweichuah

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1 Comment

flowinwind Over a year ago

found out why it didnt work initially... I was incrementing the index in the wrong place lol. face palm

Cherryishappy · Accepted Answer · 2015-12-14 06:57:09Z

0

call function

Collections.sort(array, new SortData());

in SortData.java

import java.util.Comparator;

import tg.cw.pd.model.ModelcurrentMin;

public class SortData implements Comparator<Object>
{
    public int compare(Object o1, Object o2) 
    {

        int result;

        String desc1 = ((ModelcurrentMin)o1).getcurrentMin();
        String desc2 = ((ModelcurrentMin)o2).getcurrentMin();

        result = desc1.compareTo(desc2);    //asc
        return   result;
   }
}

answered Dec 14, 2015 at 6:57

Cherryishappy

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Comments

Ramesh-X · Accepted Answer · 2015-12-14 06:57:38Z

Check this one..

public static void main(String[] args) {
    int[] array = new int[]{3, 4, 2, 7, 1, 5, 6};
    System.out.println(Arrays.toString(array));   //[2, 4, 3, 7, 5, 1, 6]

    selectionSort(array);                         
    System.out.println(Arrays.toString(array));   //[1, 4, 3, 7, 5, 2, 6]

    selectionSort(array);                         
    System.out.println(Arrays.toString(array));   //[1, 2, 3, 7, 5, 4, 6]

    selectionSort(array);                        
    System.out.println(Arrays.toString(array));   //[1, 2, 3, 4, 5, 7, 6]

    selectionSort(array);                      
    System.out.println(Arrays.toString(array));   //[1, 2, 3, 4, 5, 6, 7]
}

private static void selectionSort(int[] array) {
    for (int index = 0; index < array.length; index++) {
        int currentMin = array[index];
        int indexOfMin = index;
        boolean swapNeeded = false;

        for (int j = index + 1; j < array.length; j++) {
            if (array[j] < currentMin) {
                currentMin = array[j];
                indexOfMin = j;
                swapNeeded = true;
            }
        }
        if (swapNeeded) {
            swap(array, index, indexOfMin);
            return;
        }
    }
}

private static void swap(int[] a, int i, int j) {
    int temp = a[i];
    a[i] = a[j];
    a[j] = temp;
}

selectionSort() has to be called 7 times to sort this array.

But if you consider array like {3, 5, 1, 4, 7, 6, 2}, 3^rd and 4^rd indices of the array are already in the sorted positions. Therefore, selectionSort() has to be called only 5 times.

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