Question

I was learning about recursion and was attempting a palindrome check. It is not working. Can someone help me figure out the reason.

private static bool CheckPalin(string p)
{
    if(p.Length == 1 || p.Length == 0)  //added check for even cases
        return true;
    if(p[0] != p[p.Length -1])
        return false;

    CheckPalin(p.SubsString(1, p.Length -2));
    return true;
}

Answer 1

Dan hit one failure square on the head (as implied by my question about aa — length 0 strings will give you trouble).

The other failure case, as indicated by false positives is actually pretty obvious once you take a quick step back and look for it:

CheckPalin(p.SubsString(1, p.Length -2));
return true;

Try:

return CheckPalin(p.SubsString(1, p.Length -2));

It’s amazing, I skimmed it twice without noticing it — until you pointed out the false positives. 🙂