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javaarraystraversal
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Connecting life with Android

Reputation: 3926

java array traversal in circular manner

I have an array which have 1 2 3 4 5 values.

array a = [ 1 , 2, 3, 4, 5]

Now i want to traverse it in circular manner. like i want to print 2 3 4 5 1 or 3 4 5 1 2 or 5 1 2 3 4 and so on. any algorithm on this?

Edit: I want to print all the combination in circular manner. i don't want to state starting point at its initial phase.

Upvotes: 12

Views: 18790

Answers (6)

Stephen C
Stephen C

Reputation: 718826

int start = ...
for (int i = 0; i < a.length; i++) {
    System.out.println(a[(start + i) % a.length]);
}

(If you want to iterate the array backwards from start, change start + i to start - i + a.length in the array subscript expression. The + a.length is needed because, in Java, x % y is negative when x is negative; see Best way to make Java's modulus behave like it should with negative numbers?)

I should note that this is probably not the most efficient way of expressing the loop ... in terms of execution speed. However, the difference is small, and most likely irrelevant.

A more relevant point is whether using % in this way gives more readable code. I think it does, but maybe that's because I've seen / used this particular idiom before. Maybe a comment would be warranted.

Upvotes: 27

FrankelStein
FrankelStein

Reputation: 990

Instead of using a for loop with indexes, which is harder to read, you can use Iterables from Google Guava as follows :

List<Integer> myList = List.of(1,2,3);
Iterator<Integer> myListIterator = Iterables.cycle(myList).iterator();

then you will only have to use myListIterator.next(). example :

System.out.println(myListIterator.next());
System.out.println(myListIterator.next());
System.out.println(myListIterator.next());
System.out.println(myListIterator.next());

This will print : 1 2 3 1

Upvotes: 0

softerboy
softerboy

Reputation: 11

In addition to Stephen C's answer

int start = ...

for (int i = 0; i < a.length; i++) {
    System.out.println(a[(start - i + a.length) % a.length]);
}

Use this for reverse loop from start index. It's a little unclear, but in some cases very useful. For example: UI components like carousel.

And there's no ArrayIndexOutOfBoundsException!!!

Upvotes: 1

Rangi Lin
Rangi Lin

Reputation: 9451

Basically you just need to loop through the array, and change the current index if necessary (like move it to the start of the array when it meets the end)

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

private static String printCircularly(int[] array, int startIndex) {
    StringBuilder sb = new StringBuilder();
    int currentIndex = startIndex;
    do {
        sb.append(array[currentIndex++]);
        if (currentIndex > array.length - 1) {
            currentIndex = 0;
        }
    }
    while (currentIndex != startIndex);
    return sb.toString();
}

Upvotes: 1

Swagatika
Swagatika

Reputation: 3436

int st = n ; // n is the starting position from where you print
for(int i = st; i < a.length; i++)
{
   -- print each array[i];
}

if(st != 0)
{
   for(int i = 0 ; i < st ; i++)
   {
      --- print each array[i];
   }
}

Upvotes: 1

Timothy Jones
Timothy Jones

Reputation: 22125

How about the following:

int start = // start position, must be in bounds
int i = start;
do {

   ....

   i++;
   if(i == a.length) i = 0;
} while(i != start);

Upvotes: 2

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