Eliminating Recursion with Stacks

base_condition.rb

def base_condition_for_comb(n,m)
  (1 == n) || (0 == m) || (m == n)
end

comb_method_with_stacks.rb

def comb(n,m) 
  return 1 if base_condition_for_comb(n,m) 
  stack = [[n,m]] 
  result = 0 
  while !stack.empty? 
    n, m = stack.pop 
    if base_condition_for_comb(n,m) 
      result += 1 
    else 
      stack.push([n-1, m]) 
      stack.push([n-1, m-1]) 
    end 
  end
  result 
end

complete_comb_method.rb

def base_condition_for_comb(n,m)
  (1 == n) || (0 == m) || (m == n)
end

def comb(n,m)
  return 1 if base_condition_for_comb(n,m)
  stack = [[n,m]]
  result = 0
  while !stack.empty?
    n, m = stack.pop
    if base_condition_for_comb(n,m)
      result += 1
    else
      stack.push([n-1, m])
      stack.push([n-1, m-1])
    end
  end
  result
end

original_method.rb

def comb(n,m)
  if (1 == n) || (0 == m) || ( m == n)
    return 1
  else
    return (comb(n-1), m) + comb(n-1, m-1))
  end
end