Why the same algorithm does not print out the input array ?

[tangara goh]

Today, I practised more algorithms and I am stumped by this same algorithm that gives a different result

public class workingSolutiontoPrintInputArraywhenSorting {
 
public static void insertionSortPart2ArrayList(ArrayList<Integer>arr) {
    for(int i = 1; i < arr.size(); i++) {
        int j = i;
        int value = arr.get(i);
            while(j >=1  && arr.get(j-1) > value) {
            arr.set(j, arr.get(j - 1));
            j--;
        }
        arr.set(j, value);
        print(arr);
        }
    }

public static void print(ArrayList<Integer> arr) {
        for(int i: arr)
            System.out.print(i + " ");      
        System.out.println();
    }
 
 
public static void insertionSortPart2ArrayList(ArrayList<Integer>arr) {
    for(int i = 1; i < arr.size(); i++) {
        int j = i;
        int value = arr.get(i);
    //  while(j >=i  && arr.get(j-1) > value) {
            while(j >=1  && arr.get(j-1) > value) {
            arr.set(j, arr.get(j - 1));
            j--;
        }
        arr.set(j, value);
        print(arr);
        }
    }
 
 
public static void main(String[] args)  {
 
        ArrayList<Integer> unsortedArray = new ArrayList<Integer>();
        unsortedArray.add(1);
        unsortedArray.add(4);
        unsortedArray.add(3);
        unsortedArray.add(5);
        unsortedArray.add(6);
        unsortedArray.add(2);
        ArrayList<Integer>Hacker = new ArrayList<Integer>();
        Hacker.add(4);
        Hacker.add(3);
        Hacker.add(2);
        Hacker.add(1);
        int[]arr = {1, 4, 3, 5, 6, 2}; 
        insertionSortPart2ArrayList(unsortedArray);//works
        insertionSortPart2ArrayList(Hacker);//does not print out the input array

Hope someone can explain where did i go wrongly. Again, my heartfelt thanks to this forum members who have been coaching me so much.

[Piet Souris]

And we will keep helping you for as long as you need us!

But if I run your code (after outcommenting the second sort-routine, since that is a duplicate of the first) I get this result:

1 4 3 5 6 2
1 3 4 5 6 2
1 3 4 5 6 2
1 3 4 5 6 2
1 2 3 4 5 6
3 4 2 1
2 3 4 1
1 2 3 4

And that seems okay to me.

[Piet Souris]

And if you want to start with printing the input arrayList, then add this line:

print(arr);

at line 3 and a half.

[tangara goh]

Piet Souris wrote:And we will keep helping you for as long as you need us!

But if I run your code (after outcommenting the second sort-routine, since that is a duplicate of the first) I get this result:


3 4 2 1
2 3 4 1
1 2 3 4

And that seems okay to me.

It should print out 4 3 2 1 but it doesn't.  This is the part that puzzles me.

[Piet Souris]

Try this:

public static void insertionSortPart2ArrayList(ArrayList<Integer> arr) {
    System.out.println("inputlist");
    print(arr);
    System.out.println("------------------------");
    for (int i = 1; i < arr.size(); i++) {
        int j = i;
        int value = arr.get(i);
        System.out.println("going to put element " + value + " in its correct place:");
        while (j >= 1 && arr.get(j - 1) > value) {
            arr.set(j, arr.get(j - 1));
            j--;
        }
        arr.set(j, value);
        print(arr);
        System.out.println("---------------------");
    }
    System.out.println("finished");
}

[Piet Souris]

Did you figure out the answer to your question?

In your code, the first arraylist printed is the arraylist after the first switch from element 1 and element 0.

Now, in that first list, since 4 > 1, no switch took place and so it looks as if the inputlist is printed. In the second arraylist, 4 > 3, so these get swapped and therefore it seems as if now the inputlist is NOT shown.

In the snippet that I gave, you can follow exactly what happens during the sort.

[tangara goh]

Piet Souris wrote:Did you figure out the answer to your question?

In your code, the first arraylist printed is the arraylist after the first switch from element 1 and element 0.

Now, in that first list, since 4 > 1, no switch took place and so it looks as if the inputlist is printed. In the second arraylist, 4 > 3, so these get swapped and therefore it seems as if now the inputlist is NOT shown.

In the snippet that I gave, you can follow exactly what happens during the sort.

Without what you have pointed out to me, I would be clueless till today.  Thank you so much.

Now, I tried to put in :

if(a.get(0) > a.get(1)) {
			System.out.println(a);
		}

But, it will be printed with the brackets.  Now, there are solutions offered by stackoverflow like this one

https://stackoverflow.com/questions/32774059/output-arraylist-to-string-without-brackets-appearing

I just wonder if there is anything that can be added to the code that it will print out the array without what is suggested in SO or another way to do this insertion sort without adding those lines above ?

Really, i find all these hackerRank questions very tricky but once again thank you all the great people here.

[Piet Souris]

hi Tangara,

at StackOverflow several methods are given to print the arraylist in several ways. How would you like the list to be printed (can you give an example) and under what condition do you want that print? Only when a.get(0) > a.get(1)?