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

Create a simple range type which contains start / end of range values. Add a constructor which takes only one value and sets start = end = value. Maintain a stack of range objects, work your way through a sorted copy of the array, extend the top range or add a new range as appropriate. More specifically, when the value in the array is 1 + the end value for the range object on the to of the stack, increment the end value for that range, when it's not, push a new range (with start = end = value at index in array) onto the stack.