From: pedro oliva <lists@...>
Date: 2013-06-06T09:19:47+09:00
Subject: Need help understanding recursion.

Ive been reading Chris Pine's book 'Learn to Program' and its been going
great up until I got to chapter 10 on recursion and thus has completely
taken all my excitement from going forward. I understand that recursion
is a method that will continue to call itself till there is an attribute
to cause it to exit the loop. The example in the book though has me all
sorts of confused. Can someone walk me through the example and bring
back the excitement to continue to learn Ruby!



M = 'land'
o = 'water'

world = [
  [o,o,o,o,o,M,o,o,o,o,o],
  [o,o,o,o,M,M,o,o,o,o,o],
  [o,o,o,o,o,M,o,o,M,M,o],
  [o,o,o,M,o,M,o,o,o,M,o],
  [o,o,o,o,o,M,M,o,o,o,o],
  [o,o,o,o,M,M,M,M,o,o,o],
  [M,M,M,M,M,M,M,M,M,M,M],
  [o,o,o,M,M,o,M,M,M,o,o],
  [o,o,o,o,o,o,M,M,o,o,o],
  [o,M,o,o,o,M,M,o,o,o,o],
  [o,o,o,o,o,M,o,o,o,o,o]]

def continent_size world, x ,y

  if x < 0 or x > 10 or y < 0 or y > 10
    return 0
  end

  if world[y][x] != 'land'
    return 0
  end

  size = 1
  world [y][x] = 'counted land'

  size = size + continent_size(world, x-1, y-1)
  size = size + continent_size(world, x , y-1)
  size = size + continent_size(world, x+1, y-1)
  size = size + continent_size(world, x-1, y )
  size = size + continent_size(world, x+1, y )
  size = size + continent_size(world, x-1, y+1)
  size = size + continent_size(world, x , y+1)
  size = size + continent_size(world, x+1, y+1)
  size

end

puts continent_size(world, 5, 5)

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