Java Recursion output

Question

I have this recursion here, when I input "ello", the output returns "ello". I thought it would return "ellllloo". Am I not following the recursion right? It's keep calling FN(str.substring(1));

            return str.substring(0, 1) + FN(str.substring(1));

Side note: you can use 'isEmpty()' instead of querying the length and comparing to 0. And you might want to rework your question until it becomes clear what exactly your recursion should yield as output. Right now, the only thing that can be said is: your recursion is based on letters being a or h; and both letters do not show up in your input. So you always take the "then" path of the second if. What is the surprise there? — GhostCat
– GhostCat, Commented May 5, 2015 at 11:16
return str.substring(0, 1) + FN(str.substring(1)). yes, so with this "ello", it returns "el"+FN("llo"), and so on, that wouldn't output "ello", but I'm getting "ello" in the output — Robert
– Robert, Commented May 5, 2015 at 11:25

Othman Benchekroun · Accepted Answer · 2015-05-05 11:21:55Z

4

There is no 'a' or 'h' in the input, so it will always call return str.substring(0, 1) + FN(str.substring(1)); until the length is 0 :

FN("ello") = 
   "e" + FN("llo") = 
   "e" + "l" + FN("lo") = .... = "ello"

answered May 5, 2015 at 11:21

Othman Benchekroun

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user4624062 · Accepted Answer · 2015-05-05 11:23:16Z

1

Use

str.substring(0, 2)// instead of str.substring(0, 1)

answered May 5, 2015 at 11:23

user4624062

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singhakash · Accepted Answer · 2015-05-05 11:42:00Z

1

Your recursion each time takes the first letter of the remaining string:

  "e" + FN("llo")
= "e" +    "l"   + FN("lo") 
= "e" +    "l"   + "l"     + FN("o") = "ello"

edited May 5, 2015 at 11:42

singhakash

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answered May 5, 2015 at 11:22

vojta

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