Some more advanced recursion

Question

I've been looking around for awhile now, and I haven't found anything that helped me. I have to write a program that uses one method (the main method) to read in the size of/and elements of an array. Then I must write a recursive method titled "forwardsEqualBackwards" which returns true if the elements of the array can be read the same way regardless of whether the array is read forwards or backwards (it's a a test to see whether or not it's a palindrome) and false otherwise.

See this link: http://stackoverflow.com/questions/4367260/creating-a-recursive-method-for-palindrome-in-java — Maroun, Nov 29 '12 at 07:38

score 2 · Answer 1 · answered Nov 29 '12 at 07:36

2

pseudocode:

bool forwardsEqualBackwards(array a, int length, int indexToLookAt=0)
{
  if (indexToLookAt >= length-indexToLookAt-1)
    return true; //reached end of recursion
  if (a[indexToLookAt] == a[length-indexToLookAt-1])
    return forwardsEqualBackwards(a,length, indexToLookAt+1); //normal recursion here
  else 
    return false;
}

forwardsEqualBackwards("",0);  //returns true
forwardsEqualBackwards("a",1);  //returns true
forwardsEqualBackwards("otto",4);  //returns true
forwardsEqualBackwards("otsto",5);  //returns true
forwardsEqualBackwards("otstou",5);  //returns false

answered Nov 29 '12 at 07:36

Philipp

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Apologies. It has to be a static recursive method. Still. This was very helpful and I thank you. What I don't understand is that the array won't read into the recursive method from the main method. So I can't look at the contents of the array within the recursive method. – Christopher Lhama Rowse Nov 29 '12 at 07:39
this is pseudo code. You can make the method static if you want. Either you pass the array as an argument (as I did) or you have a static variable which is accessed by both main and the recursive function. – Philipp Nov 29 '12 at 07:46

score 1 · Answer 2 · answered Nov 29 '12 at 07:37

1

bool method(int start, int end)
{
     if(start<=end)
     {
           if(Array[start]!=array[end])
                 return false;
           return method(start+1, end-1)
     }
     return true;

}

answered Nov 29 '12 at 07:37

Muhammad Tauseef

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Some more advanced recursion

2 Answers2