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

Python (>= 2.6)

This version additionally handles duplicates and unsorted sequences.

from __future__ import print_function

def ranges(a):
    a.sort()
    i = 0
    while i < len(a):
        start = i
        while i < len(a)-1 and a[i] >= a[i+1]-1:
            i += 1
        print(a[start] if a[start] == a[i] else "%d-%d" % (a[start], a[i]),
              end="," if i < len(a)-1 else "\n")
        i += 1

Example:

import random
r = range(10)
random.shuffle(r)
ranges(r)
ranges([1,3,4,5,6,8,11,12,14,15,16]);
ranges([])
ranges([1])
ranges([1, 2])
ranges([1, 3])
ranges([1, 3, 4])
ranges([1, 2, 4])
ranges([1, 1, 2, 4])
ranges([1, 2, 2, 4])
ranges([1, 2, 2, 3, 5, 5])

Output:

0-9
1,3-6,8,11-12,14-16
1
1-2
1,3
1,3-4
1-2,4
1-2,4
1-2,4
1-3,5