based on recursion using java

Question

public void length() {
    System.out.println(length(head, 0));
}
public int length(Node he, int count) {
    if(he!=null) {
        // System.out.println(he.data +"   "+count++);
        // count++;
        // return length(he.next, count);
        return length(he.next, count++);
    }
    return count;
}

In the code above, I have to find the length of linked list. If I run the same code, I am getting the length 0.But, when i use commented code and I am getting the correct length. Why is that happening?

count++ actually passes count, see this Question how post Increment works — SomeJavaGuy
– SomeJavaGuy, Commented Aug 11, 2016 at 7:12
What about removing the second parameter and simply return (he == null) ? 0 : 1 + length(he.next);? — fabian
– fabian, Commented Aug 11, 2016 at 7:20
thanks @fabian .. I actually found other way through you. :) — Krishna krish
– Krishna krish, Commented Aug 11, 2016 at 9:00

Eran · Accepted Answer · 2016-08-11 07:12:30Z

5

length(he.next, count++) passes the original value of count to the method call, since you are using the post increment operator. Therefore you are always passing 0.

length(he.next, ++count) would work, since here the incremented value of count will be passed.

In your commented code you are not passing the value of count++ to the method call, you are passing count after it was already incremented, which also works.

answered Aug 11, 2016 at 7:12

Eran

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3 Comments

Krishna krish Over a year ago

but, the code is recursing and for the next recursio step.. it has to increment right? as like waht happens in iterative steps? why didn't that happen in recursion?

Eran Over a year ago

@Krishnakrish I'm not sure what you mean. You are passing the un-incremented value of count to each recursive call. The only reason your recursion ends (instead of producing StackOverflowError) is that the stopping condition depends on the passed Node (which advances in each recursive call) and not on the passed count (which is always 0).

JavaHopper Over a year ago

@Eran, looks like he is expecting the value to be incremented after the previous call stack completes, which is not the case. The variables passed as arguments to a recursive method are part of only that particular recursion call stack

burakozgul · Accepted Answer · 2016-08-11 08:04:34Z

0

Use

return length(he.next, ++count);

or

System.out.println(he.data +"   "+count);
count++;
return length(he.next, count);

I will try to simulate your and my code.

Your code :

//count = 0

length(he.next, count++) // length(he.next, 0) 

//after recursion call count increments , count = 1

My code :

//count = 0

// before recursion call, ++count increments count 

// count = 1 

length(he.next, ++count) // length(he.next, 1)

Guys im new here if im wrong, please edit me :)

edited Aug 11, 2016 at 8:04

answered Aug 11, 2016 at 7:16

burakozgul

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2 Comments

Krishna krish Over a year ago

but, the code is recursing and for the next recursio step.. it has to increment right? as like waht happens in iterative steps? why didn't that happen in recursion?

burakozgul Over a year ago

Yes you need to increment. Actually you are incrementing count but incrementation happens after recursion call. Because of that you are passing old value of count which is 0.

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