Question

def recursive_insert(arr)
  return arr if arr.size<=1
  recursive_insert(arr[0,arr.size-1])
  i=arr.size-1
  while arr[i-1]>arr[i] and i>0
    arr[i],arr[i-1] = arr[i-1],arr[i]
    i-=1
  end
  arr
end
arr=[5,4,3,2,6,1]
x=recursive_insert(arr)
puts x.inspect

This doesn’t work. I suspect that Ruby has a pass by reference mechanism, which prevents my arr variable being updated for each recursive call.

How do I solve this? I have so many difficulties writing a recursive function in Ruby.

Answer 1

This:

arr[0, arr.size - 1]

returns a copy of part of arr and changes to that copy will not be reflected in arr. So, your recursive step does nothing useful and your method is equivalent to this:

def recursive_insert(arr)
  return arr if arr.size<=1
  i=arr.size-1
  while arr[i-1]>arr[i] and i>0
    arr[i],arr[i-1] = arr[i-1],arr[i]
    i-=1
  end
  arr
end

and that gets the 1 in the right place and that’s all.