From: Jeffrey Dik <jeffrey.dik@...>
Date: 2004-07-11T17:22:50+09:00
Subject: Re: A little algorithmic help requested...

On Sun, Jul 11, 2004 at 04:10:34PM +0900, Hal Fulton wrote:
> Here's a problem my tired brain is having trouble with.
> 
> Given a sorted array of integers, convert them into as many
> ranges as possible (ranges of three or more).
> 
> Example:
> [1,2,3,4,6,7,8,11,12,15,16,17] ==> [1..4,6..8,11,12,15..17]
> 
> How would *you* do this?

At 4:20am, I'd do it like this

        a = [1,2,3,4,6,7,8,11,12,15,16,17]
        
        def to_ranges(a)
          ranges = [a[0]..a[0]]
          a.shift
          a.each_index { |i|
            if ranges.last.last + 1 == a[i]
              ranges[-1] = ranges.last.first..a[i]
            else
              ranges.push(a[i]..a[i])
            end
          }
          ranges.map! { |r|
            case r.last-r.first
            when 0
              r = r.first
            when 1
              r = [r.first, r.last]
            end
        
            r
          }
          ranges.flatten
        end
        
        puts to_ranges(a)

I'm guessing I'd do it differently at a some other time in the day :-)

Sleepy time,
Jeff

> 
> 
> Thanks,
> Hal
> 
> 
>