From: steve ross <cwdinfo@...>
Date: 2010-04-24T03:48:41+09:00
Subject: Re: Best way to write this method?

On Apr 23, 2010, at 9:53 AM, Derek Cannon wrote:
> 
> def elements_overlap?(a, b)
> array = a.to_a & b.to_a
> !array.empty?
> end

Here's a simple out-of-bounds comparison for elements_overlap? It makes the decision with, at most, two comparisons.

require 'rubygems'
require 'spec'

def elements_overlap?(a, b)
 !((b.first > a.last) || (a.first > b.last))
end

describe "overlapping" do
 before(:each) do
   @a = [1, 2, 3, 4, 5]
 end

 it "should overlap if a begins before b, but ends during b" do
   elements_overlap?([1, 2, 3, 4, 5], [2, 3, 4, 5, 6]).should be(true)
 end

 it "should overlap if a begins after b, but ends after b" do
   elements_overlap?([4, 5, 6, 7], [2, 3, 4, 5, 6]).should be(true)
 end

 it "should overlap if a begins after b and ends before b" do
   elements_overlap?([4, 5], [2, 3, 4, 5, 6]).should be(true)
 end

 it "should overlap if a begins before b and ends after b" do
   elements_overlap?([1, 2, 3, 4, 5, 6, 7], [2, 3, 4, 5, 6]).should be(true)
 end

 it "should not overlap if a begins before b and ends before b" do
   elements_overlap?([1, 2], [3, 4, 5, 6]).should be(false)
 end

 it "should not overlap if a begins after b and ends after b" do
   elements_overlap?([7, 8], [3, 4, 5, 6]).should be(false)
 end
end