Generate all contiguous sequences from an array

Question

There's an array say [1,2,4,5,1]. I need to print all the contiguous sub-arrays from this.

Input: [1,2,4,5,1]

Output:

 1
 1,2
 1,2,4
 1,2,4,5
 1,2,4,5,1
 2
 2,4
 2,4,5
 2,4,5,1
 4
 4,5
 4,5,1
 5
 5,1
 1

I tried but couldn't get the complete series.

//items is the main array
for(int i = 0; i < items.length; i++) {
    int num = 0;
    for(int j = 0; j < items.length - i; j++) {
        for(int k = i; k < j; k++) {
            System.out.print(items[k]);
        }
        System.out.println();
    }
}

Solution 1

You only have to make 2 changes. The outer loop iterates as much times as the array has elements, this is correct. The first inner loop should use the index of the outer loop as start index (int j = i), otherwise you always start with the first element. And then change the inner loop break conditon to k <= j, otherwise i does not print the last element.

// i is the start index
for (int i = 0; i < items.length; i++)
{
    // j is the number of elements which should be printed
    for (int j = i; j < items.length; j++)
    {
        // print the array from i to j
        for (int k = i; k <= j; k++)
        {
            System.out.print(items[k]);
        }
        System.out.println();
    }
}

Solution 2

Tested and working! Try this algorithm.

for(int i=0;i<items.length;i++) {

        for(int j=i;j<items.length;j++) {

            for(int k=i;k<=j;k++) {

                System.out.print(items[k]);
            }
            System.out.println();
        }
}

Comments

[kai]

No it does not work. It prints the whole array, then only the last four elements, then the last three elements and so on...

[kai]

The output is correct, but with much extra spaces between the lines :)

[Young Song]

Using loop twice. To get just sum, I suggested using pattern of the subarrays.

[Ali Akram]

is it possible to do in less than 3 loops?

[kai]

@AliAkram This algorithm has a runtime complexity of O(n²) so you need at least two loops. My code uses only two loops for generating the sequences. The third loop is only for printing. You can replace the inner loop with System.out.println(Arrays.toString(Arrays.copyOfRange(items, i, j + 1)));

[chirag soni]

@AliAkram yes possible to use less than 3 loops. Look here: stackoverflow.com/a/70754152/11421611