Final Exam Review Fall 2003: Recursion
Questions, comments, answers?
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a) print #2, print #1, print #3
b) 5
c) def upDown(word):
if len(word)==1:
print word #Print #1
return
print word #Print #2
upDown(word[0:len(word)-1])
print word #Print #3
| Can you fix the indentation on the code? It's not right as-is. Mark Guzdial |
How about the following indentation?
c)def upDown(word):
if len(word)==1:
print word #Print #1
return
print word #Print #2
upDown(word[0:len(word)-1])
print word #Print #3
Should the print statements be indented the same amount as the def?
def upDown(word):
if len(word) == 1:
print word
return
print word
upDown(word[0:len(word)-1])
print word
Could you please explain b? Why is it 5?
Hello, ello, llo, lo, o. The program is first ran using the input "Hello". The program is called again- now using "ello". The program is called once again using "llo". And so on. Until it gets to just the letter "o". At this point, five programs are running at once. (Now the programs begin to finish one by one- so, five is maximum). I hope this helps. #12
| You can also think about it from the perspective of functional programming. Functions in functional programming tend to process one small bit of data at a time. These recursive functions work similarly, where the one small bit is each letter. Five letters, five calls to the function. Mark Guzdial |
Wouldn't you need more memory when using recursion? Would that be its downside?
- This is an off-topic question, btw.
| It depends on how the recursion is implemented and the language. Java is really bad with recursion, so it does take too much memory. Scheme is excellent with recursion, so well-written recursive functions take no more memory than a FOR loop. Mark Guzdial |
I wish my wish not be granted :-)
Here's a hint that may work with less typing!: word[:-1]
Chris Reinig
couldn't you just use the spacing that was in the example in the final review??
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