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    <p>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.</p> <p>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.</p> <p>Also, try to think in terms of collections. This always makes things clearer. The pseudo-code is something like: <code>String</code> becomes <code>List&lt;Integer&gt;</code> becomes <code>List&lt;Range&gt;</code> and finally becomes <code>String</code>.</p> <pre><code>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&lt;Integer&gt; inputNumbers = new ArrayList&lt;Integer&gt;(); 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&lt;Range&gt; ranges = new ArrayList&lt;Range&gt;(); for (Integer number : inputNumbers) { if (thisRange != null &amp;&amp; number &lt;= thisRange.getHigh() + 1) { // if we are already building a range (not null) &amp;&amp; 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&lt;String&gt; into a single String String result = StringUtils.collectionToCommaDelimitedString(ranges); System.out.println("result = " + result); } } </code></pre>
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    1. POConvert a string like 2,4,5,6,7,8,10,12,14,15,16 to 2,4-8,10,12,14-16
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    1. USSynesso
    1. USSynesso
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    1. POConvert a string like 2,4,5,6,7,8,10,12,14,15,16 to 2,4-8,10,12,14-16
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    1. COIt works fine for the string input in the ascending order but for a random sequence of string it would give a incorrect result...Can the `sortArray` function I used above be applied here? Eg: `2,5,89,23,6,45,7,8,15,16` gives `2,5,89,23,6,45,7-8,15-16` what i want is `2,5-8,15-16,23,45,89`
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      1. USSangeet Menon
    2. COYes, sort the `List<Integer>` before proceeding with the creation of `List<Range>`. I updated the answer. There is also a problem around de-duplication of numbers in the input. Can you see it?
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      1. USSynesso
    3. COI fixed the de-dupe problem.
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