Ruby infinite loop in bubble sort algorithm

Question

I have build the basic bubble sort algorithm with Ruby, without problems. The code is as follows:

def bubble_sort(arr)
 swapped=true
 while swapped
    swapped=false
    for j in 0..arr.length-2 do
      if arr[j]>arr[j+1]
        arr[j], arr[j+1] = arr[j+1], arr[j]
        swapped=true
      end
    end
 end
arr
end

Now, I am trying to implement the same method, but with a function of accepting code block. Code block part works fine, but when code block is not provided, the method should work like above, although it looks logically same to me, but for some reason, it goes into an infinite loop:

On the line of "unless", it will check for the condition and swap positions if necessary, and will skip the yield part. I tried step by step debugging by rdebugger but could not find out the reason.

def bubble_sort_by(arr)
  swapped = true
  while swapped
    swapped=false
    for i in 0..arr.length-2 do
      unless block_given?
        arr[i], arr[i+1] = arr[i+1], arr[i] if arr[i] < arr[i+1]
        swapped=true
      end #unless
    if block_given?
      if yield(arr[i], arr[i+1])>0
        arr[i], arr[i+1] = arr[i+1], arr[i]
        swapped=true
      end #if yield
    end #if block_given?
    end #for
  end #while
puts arr
return arr
end

Answer 1

Quick answer:

arr[i], arr[i+1] = arr[i+1], arr[i] if arr[i] < arr[i+1]
swapped=true

Should be replaced with:

if arr[i] < arr[i+1]
  arr[i], arr[i+1] = arr[i+1], arr[i]
  swapped=true
end

What's happening is you're always setting swapped to true, even if the elements were not swapped. So you get stuck in an infinite loop.

And now for a bit of code clean-up... First, rather than writing:

if(foo)
  # ...
end
unless(foo)
  # ...
end

Let's make it an if/else statement:

def bubble_sort_by(arr) 
  swapped = true 

  while swapped 
    swapped=false 
    for i in 0..arr.length-2 do 
      if block_given? 
        if yield(arr[i], arr[i+1])>0 
          arr[i], arr[i+1] = arr[i+1], arr[i] 
          swapped=true 
        end 
      else 
        if arr[i] < arr[i+1] 
          arr[i], arr[i+1] = arr[i+1], arr[i] 
          swapped=true 
        end 
      end 
    end #for 
  end #while 

  return arr 
end

You could re-factor it further to remove the while loop as @Aetherus suggests, but I figured you'd appreciate seeing the actual bug fixed.