Find groups of continuous integers in a list in Java

Question

I have a list of integers in order. I want to get groups of consecutive integers in the form of arrays with the 1st and last integer for each group.

For example, for (2,3,4,5,8,10,11,12,15,16,17,18,25) I want to get a list with these arrays: [2,5] [8,8] [10 , 12] [15.18] [25.25]

Here is my code:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;


public class MyRangesTest {


public static void main(String[] args) {
    //create list of integers
    List<Integer> list=Arrays.asList(2,3,4,5,8,10,11,12,15,16,17,18,25);
    System.out.println("list:" + list);


        //create a list with integers where a new sequense of consecutive integers starts or ends
        List<Integer> sublistsStarsAndEnds= new ArrayList<>();
        sublistsStarsAndEnds.add(list.get(0));//1st line (always in sublistsStarsAndEnds list)
        for (int i=1; i<list.size()-1; i++){
            if (list.get(i)>1+list.get(i-1)){
                sublistsStarsAndEnds.add(list.get(i-1));
                sublistsStarsAndEnds.add(list.get(i));
            }
        }
        sublistsStarsAndEnds.add(list.get(list.size()-1));//last line (always in sublistsStarsAndEnds list)
        System.out.println("sublistsStarsAndEnds: " + sublistsStarsAndEnds);//present the result


        //create list with arrays that represents start and end of each subrange of consequent integers
        List<Integer[]> ranges= new ArrayList<>();
        for (int i=0; i<sublistsStarsAndEnds.size()-1; i=i+2){
            Integer[] currentrange=new Integer[2];
            currentrange[0]=sublistsStarsAndEnds.get(i);
            currentrange[1]=sublistsStarsAndEnds.get(i+1);
            ranges.add(currentrange);//present the result
        }

        //present the result
        String rangestxt="";//create result text
        for (int i=0; i<ranges.size(); i++){
            rangestxt=rangestxt+ranges.get(i)[0]+ " " + ranges.get(i)[1]+ "    ";
         }        
        System.out.println("ranges: " + rangestxt);//present the result


    }

}

This code works in the general case for what I want, but when the last sequence has only 1 integer, it cannot get the correct result.

For example, when using this list: (2,3,4,5,8,10,11,12,15,16,17,18,25) instead of getting ranges [2.5] [8, 8] [10, 12] [15,18] [25,25] we get the ranges [2,5] [8,8] [10,12] [15,25].

, . sublistsStarsAndEnds. [2, 5, 8, 8, 10, 12, 15, 15, 25, 25] [2, 5, 8, 8, 10, 12, 15, 25]. , .

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P.S. - , , Python . Python, .

Answer 1

 public static void main(String[] args) {
    List<Integer> list=Arrays.asList(2,3,4,5,8,10,11,12,15,16,17,18,19,25);
    List<List<Integer>>lList=new ArrayList<List<Integer>>(); //list of list of integer
    System.out.println("list:" + list);
    int i=0;
    int start=0;
        List<Integer> sList=new ArrayList<Integer>(2);
        for(  i = 1; i <list.size();i++){

           if( list.get(i - 1) + 1 != list.get(i)){
               sList.add(list.get(start));
               sList.add(list.get(i-1));
               lList.add(sList);
               sList=new ArrayList<Integer>(2);
               start=i;

            }

        }
        sList.add(list.get(start));        // for last range
        sList.add(list.get(list.size()-1));
        lList.add(sList);


    System.out.println("Range :"+lList);
}

:

list:[2, 3, 4, 5, 8, 10, 11, 12, 15, 16, 17, 18, 19, 25]
Range :[[2, 5], [8, 8], [10, 12], [15, 19], [25, 25]]

Answer 2

, POJO Range,

static class Range {
    private int start;
    private int end;

    Range(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    public String toString() {
        return String.format("%d - %d", start, end);
    }
}

start , i-1 list.get(i - 1) + 1 != list.get(i). - ,

public static void main(String[] args) {
    List<Integer> list = Arrays.asList(2, 3, 4, 5, 8, 10, 11, 12, 15, 16,
            17, 18, 25);
    System.out.println("list:" + list);
    int start = 0;
    List<Range> ranges = new ArrayList<>();
    for (int i = 1; i < list.size(); i++) {
        if (list.get(i - 1) + 1 != list.get(i)) {
            ranges.add(new Range(list.get(start), list.get(i - 1)));
            start = i;
        }
    }
    ranges.add(new Range(list.get(start), list.get(list.size() - 1)));
    System.out.println(ranges);
}

( )

[2 - 5, 8 - 8, 10 - 12, 15 - 18, 25 - 25]

, .

Answer 3

Here is a simple algorithm that I sometimes adapt and use.

public void printRanges(int[] input) {
    if (input.length == 0)
        return;

    // Only necessary if not already sorted
    Arrays.sort(input);

    int start = input[0];
    int end = input[0];

    for (int rev : input) {
        if (rev - end > 1) {
            // break in range
            System.out.println("Range: [" + start + ", " + end + "]");
            start = rev;
        }
        end = rev;
    }
    System.out.println("Range: [" + start + ", " + end+"]");
}