How would you display an array of integers as a set of ranges? (algorithm)

Question

Given an array of integers, what is the simplest way to iterate over it and figure out all the ranges it covers? for example, for an array such as:

$numbers = ar         


        

Answer 1

My solution in Java 1.5 would be:

public static List getRanges(int... in) {
    List result = new ArrayList();
    int last = -1;
    for (int i : in) {
        if (i != (last + 1)) {
            if (!result.isEmpty()) {
                addRange(result, last);
            }
            result.add(String.valueOf(i));
        } 
        last = i;
    }
    addRange(result, last);
    return result;
}

private static void addRange(List result, int last) {
    int lastPosition = result.size() - 1;
    String lastResult = result.get(lastPosition);
    if (!lastResult.equals(String.valueOf(last))) {
        result.set(lastPosition, lastResult + "-" + last);
    }
}

public static void main(String[] args) {
    List ranges = getRanges(1, 3, 4, 5, 6, 8, 11, 12, 14, 15, 16);
    System.out.println(ranges);
}

which outputs:

[1, 3-6, 8, 11-12, 14-16]

Greetz, GHad