Question

I want to convert a string input like 2,3,6,7,8,10,12,14,15,16 to 2-3,6-8,10,12,14-16 using java

I tried using the below code

        Vector ar=new Vector();

        int lastadded=0;

        String ht="";

        String [] strarray=str.split(",");

        strarray=sortArray(strarray);

        Vector intarray=new Vector();


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

        int temp=1;
            for(int j=1;j<=intarray.size();j++)
            {
                if(Integer.parseInt(strarray[i])==Integer.parseInt(intarray.get(j-1).toString()))
                {
                 temp=0;
                }
            }
            if(temp==1)
            {
                intarray.add(Integer.parseInt(strarray[i]));
                ar.add(Integer.parseInt(strarray[i]));
            }


        }


       ht="";
       String strdemo="";
       for(int i=0;i<intarray.size();i++)
       {

            if(ht=="")
            {

                ht=ar.get(i)+"";
        lastadded=i;
            }

        else
         {
             strdemo=(String)ht;
            if(strdemo.length()==ar.get(0).toString().length())
            {

   if(Integer.parseInt(strdemo.substring(0))==Integer.parseInt(ar.get(i).toString())-1)
             {
                 strdemo=strdemo+"-"+ar.get(i);
                 lastadded=Integer.parseInt(ar.get(i).toString());
                 ht=strdemo;
             }
             else
             {
                 strdemo=strdemo+","+ar.get(i);
                 lastadded=Integer.parseInt(ar.get(i).toString());
                 ht=strdemo;
             }
            }
            else if(strdemo.length()==3)
            {
                 strdemo=(String)ht;
                 if(Integer.parseInt(strdemo.substring(strdemo.length()-1,strdemo.length()))==Integer.parseInt(ar.get(i).toString())-1)
                 {
                     strdemo=strdemo.substring(0,strdemo.length()-2)+"-"+Integer.parseInt(ar.get(i).toString());
                     lastadded=Integer.parseInt(ar.get(i).toString());
                     ht=strdemo;
                 }
                 else
                 {
                     strdemo=strdemo+","+Integer.parseInt(ar.get(i).toString());
                     lastadded=Integer.parseInt(ar.get(i).toString());
                     ht=strdemo;
                 }
            }//Else IF
            else{
                strdemo=(String)ht;
                int de=1;


                int ddd=lastadded;
                 if(ddd==Integer.parseInt(ar.get(i).toString())-1)
                 {
                      int lastaddedlen=(lastadded+"").length();
                      String symbol=strdemo.substring(strdemo.length()-lastaddedlen-1,strdemo.length()-lastaddedlen);
                     if(symbol.equalsIgnoreCase("-"))
                       strdemo=strdemo.substring(0,strdemo.length()-lastaddedlen-1)+"-"+Integer.parseInt(ar.get(i).toString());
                     else
                     strdemo=strdemo+"-"+Integer.parseInt(ar.get(i).toString());
                     lastadded=Integer.parseInt(ar.get(i).toString());
                     ht=strdemo;
                 }
                 else
                 {
                     strdemo=strdemo+","+Integer.parseInt(ar.get(i).toString());
                     lastadded=Integer.parseInt(ar.get(i).toString());
                     ht=strdemo;
                 }
            }
    }
}

Here sortArray function sorts the array descending and returns

protected static String[] sortArray(String ss[])
    {
        String temp;
        for(int i=0;i<ss.length;i++)
        {
            for(int j=0;j<ss.length;j++)
            {
             if(Integer.parseInt(ss[i])<Integer.parseInt(ss[j]))
             {
                temp=ss[i];
                ss[i]=ss[j];
                ss[j]=temp;
             }
            }
        }
        return ss;
    }

I am not getting consistant results for some inputs for example for the below case
2,3,6,7,8,10,12,14,15,16 it gives 2-3,6-8,10,12,14-16 (which is correct)
while for 2,4,5,6,7,8,10,12,14,15,16 it gives 2-8,10,12,14-16 (which actually should have been 2,4-8,10,12,14-16)

Where does the code go inconsistent is what I need to find out..

Answer 1

This is pretty ugly and verbose in Java, but here is a version. Note, it uses StringUtils from Spring at the very end for the trivial but also ugly process of converting a String collection to a comma delimited string.

The key is to use a separate class to model the numeric ranges. Let this class know how to turn itself into a String. Then you won’t have so much logic around appending to a StringBuilder.

Also, try to think in terms of collections. This always makes things clearer. The pseudo-code is something like: String becomes List<Integer> becomes List<Range> and finally becomes String.

public class Ranges {

    // A class that models a range of integers
    public static class Range {
        private int low;
        private int high;

        public Range(int low, int high) {
            this.low = low;
            this.high = high;
        }

        public int getHigh() {
            return high;
        }

        public void setHigh(int high) {
            this.high = high;
        }

        @Override
        public String toString() {
            return (low == high) ? String.valueOf(low) : String.format("%d-%d", low, high);
        }
    }

    public static void main(String[] args) {
        String input = "2,3,6,7,8,10,12,14,15,16";

        // Turn input string into a sorted list of integers
        List<Integer> inputNumbers = new ArrayList<Integer>();
        for (String num : input.split(",")) {
            inputNumbers.add(Integer.parseInt(num));
        }
        Collections.sort(inputNumbers);

        // Flatten list of integers into a (shorter) list of Ranges
        Range thisRange = null; // the current range being built
        List<Range> ranges = new ArrayList<Range>();
        for (Integer number : inputNumbers) {
            if (thisRange != null && number <= thisRange.getHigh() + 1) {
                // if we are already building a range (not null) && this new number is 
                // the old high end of the range + 1, change the high number.
                thisRange.setHigh(number);
            } else {
                // create a new range and add it to the list being built
                thisRange = new Range(number, number);
                ranges.add(thisRange);
            }
        }

        // Join List<String> into a single String
        String result = StringUtils.collectionToCommaDelimitedString(ranges);
        System.out.println("result = " + result);
    }
}