Sunday, December 18, 2011

Majority Voting

I saw this one over at Programming Praxis. It's pretty simple with ruby, but there's one slightly interesting piece in there that might come in handy sometime. Here's the code ...

def majority(l)
h =
l.each { |v| h[v] += 1 }
max = h.max {|a,b| a[1] <=> b[1]}
max[1] >= l.length / 2.0 ? "#{max[0]} won with #{max[1]} out of #{l.length} total votes" : "No winner"

v1 = %w[A A A C C B B C C C B C C]
v2 = %w[A B C A B C A]

puts "v1 = #{majority(v1)}"
puts "v2 = #{majority(v2)}"

OK, so we create a Hash where the value in the key/value pair is initialized to 0 and we add one each time time we see a vote. Here's the cool part, we use the max function from Enumerable knowing that max itself uses each which will give us the key/value pair as a two element array. So, we set the function to compare the second element, the value, of the pair. The max that gets returned will also be a two element array and we use that to calculate whether there's a winner or not.

These types of problems are great for sharpening your programming skills in general and your ruby skills in particular. They're exactly the types of questions that end up on programming interview tests.

Let me know if you have questions or comments.