2

I'm looking to move things around within an Array.

I want to be able to move the last item within the given Array to a spot while moving those in the current location to the right. I want it to move from the first spot to the second, etc. without replacing the item that is currently there.

ex)

a,b,c,d,e

Say I want to move to "3" - it would then become

a,b,c,e,d

I currently have the following:

public static void moveLastup(String[] stuff, int position) 
{
    String y = stuff[stuff.length-1];

    for (int x = stuff.length-1; x > position; x--) 
        list[x] = list[x-1];

    stuff[position] = y;
}

edit: sorry I don't think I was clear enough. What I want to be able to do is given this method, I should be able to move the last piece anywhere. 

for (int pos = 0; pos < stuff.length; pos++)
{
    moveLastup(list,pos);
    showList(list);
}

Now when I execute this, it simply takes the last item in the next list in the for loop ex)

e,a,b,c,d

e,d,a,b,c

e,d,c,b,a

i would like it to show

e,a,b,c,d

a,e,b,c,d

a,b,e,c,d
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0

6 Answers 6

Reset to default
3

I know the question is about Arrays - don't wanna start a discussion about performance "versus" issues and "why I'm using pure array" - but for those using List I think this might be useful.

java.util.Collections.rotate method. Yeah, the name is weird, by check it out a part of the javadoc:

Note that this method can usefully be applied to sublists to move one or more elements within a list while preserving the order of the remaining elements. For example, the following idiom moves the element at index j forward to position k (which must be greater than or equal to j):

    Collections.rotate(list.subList(j, k+1), -1);

To make this concrete, suppose list comprises [a, b, c, d, e]. To move the element at index 1 (b) forward two positions, perform the following invocation:

    Collections.rotate(l.subList(1, 4), -1);

The resulting list is [a, c, d, b, e].

To move more than one element forward, increase the absolute value of the rotation distance. To move elements backward, use a positive shift distance.

public void moveElement(List list, int a, int b) {
    // forward or backward
    int direction = a > b ? 1 : -1;
    // always from minor to major to subList
    int minor = a < b ? a : b;
    int major = b > a ? b : a;
    Collections.rotate(list.subList(minor, major + 1), direction);
}
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Comments

2

Here's a more efficient and concise solution, relying on the natively implemented System.arraycopy:

public static void moveLastup(String[] arr, int pos) {
    String last = arr[arr.length-1];

    // Copy sub-array starting at pos to pos+1
    System.arraycopy(arr, pos, arr, pos + 1, arr.length - pos - 1);

    arr[pos] = last;
}

And some test code:

public static void main(String[] args) {
    String[] test = { "one", "two", "three", "four", "five" };

    // Move "five" to index 2
    moveLastup(test, 2);

    // [one, two, five, three, four]
    System.out.println(Arrays.toString(test));
}

Regarding your edit: You're working with and modifying the original array. If you want to "start over" in each moveLastup you need to work on a copy. This snippet prints what you want:

String[] list = { "a", "b", "c", "d", "e" };

for (int pos = 0; pos < list.length; pos++) {
    String[] tmpCopy = list.clone();
    moveLastup(tmpCopy, pos);
    showList(tmpCopy);
}

Output:

[e, a, b, c, d]
[a,e, b, c, d]
[a, b,e, c, d]
[a, b, c,e, d]
[a, b, c, d,e]

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3 Comments

Are you serious? Thats what I wrote 10 mins ago, and also you did x>=position and that is a waste.
is there any way to alter the original method rather than the second for statement to make it display that "starting over"?
Well, not really. You would need to "undo" the previous lastMoveup before doing the next.
1

First of all, in your code you do 

for (int x = stuff.length-1; x > pos; x--)

where pos is not even defined, I suggest on changing it to position. second of all, change the "list" to "stuff".

Modified, working code:

public static void moveLastup(String[] stuff, int position) 
    {
        String y = stuff[stuff.length-1];

        for (int x = stuff.length-1; x > position; x--)  
            stuff[x] = stuff[x-1];

        stuff[position] = y;
    }
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Comments

1

Any particular reason you're not using a List<String> instead of String[]? It'll make these type of operations easier. With an ArrayList<String>, all you need is:

list.add(3, list.remove(list.size() - 1));

Or even shorter if you used a LinkedList<String>:

list.add(3, list.removeLast());

Here's a more complete example based on yours:

LinkedList<String> list = new LinkedList<String>();
list.addAll(Arrays.asList("a", "b", "c", "d", "e"));
list.add(3, list.removeLast());
System.out.println(list); // prints "[a, b, c, e, d]"
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0

Another short and quick solution based on System.arraycopy:

System.arraycopy(array, insert, array, insert+1, array.length-insert-1);

The array content is "pushed to the right" from index "insert".

Here's some demonstration code:

int[] array = {1,2,3,4,5};
int insert = 2;
int last = array[array.length-1];
System.arraycopy(array, insert, array, insert+1, array.length-insert-1);
array[insert] = last;
for (int value:array) System.out.println(value);
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0

you could do like this:

char arr1[]=new arr1[5]; // arr1 contains a,b,c,d,e in order
char arr2[]=new arr2[5];

for(int i=0;i<arr1.length;i++) {       // copy contents to arr2
   arr2[i]=arr1[i];
}

for(int i=0,j=4;i<arr1.length;i++) {
  arr2[i]=arr1[4];
  arr2[i+1]=arr1[4];
  arr2[i+2]=arr1[i+1];
  arr2[i+3]=arr1[i+2];
  arr2[i+4]=arr1[i+3];
}

for(int i=0;arr2.length;i++) {          // Final result
  System.out.println(arr[i]+" ");
}
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