Ruby Recursion doesn't work?

Question

I was trying to make a recursive algorithm with Ruby and I couldn't do it so I kept popping the stack as it were and each time I tried a simpler recursive algorithm to see where my mistake was..

But I arrived at this:

def fact(n)
  if n==0
    1
  else
    fact(n)*fact(n-1)  
  end
end

puts fact(5)

and

ruby/part2.rb:81: stack level too deep (SystemStackError)

Ok what is going on?

Is it not possible to make recursive algorithms in Ruby??

Answer 1

your algorithm is incorrect, it should look like this

def fact(n)
  if n==0
    1
  else
   n*fact(n-1)  
  end
end

puts fact(5)

Answer 2

fact(n) * fact(n - 1) is infinite recursion. You need to reduce the problem size in each call.

def fact(n)
  if n <= 0
    1
  else
    n * fact(n - 1)  
  end
end

---

Or simply,

def fact(n)
  n <= 0 ? 1 : n * fact(n - 1)  
end

Answer 3

您必须执行诸如fact（n-1）* fact（n-2）之类的操作，因为否则，将永远调用fact（n），n = 5。