Recursion

[case.learning]

Hi everyone,

I'm a C++ novice. I'm trying to learn recursion and have written this
piece of code but it doesn't work. Could you help me to see where it
goes wrong? Thanks.

bool PalindromeHelper(string s)
{
int len = s.length();
if (len == 1 || len == 0)
return true;
else
return (s[0] == s[len-1]) &&
PalindromeHelper(s.substr(1, len-2));
}

 

[osmium]

I'm a C++ novice. I'm trying to learn recursion and have written this
piece of code but it doesn't work. Could you help me to see where it
goes wrong? Thanks.

bool PalindromeHelper(string s)
{
int len = s.length();
if (len == 1 || len == 0)
return true;
else
return (s[0] == s[len-1]) &&
PalindromeHelper(s.substr(1, len-2));
}

If the first char is not equal to the last char you sould return
immediately. Once false, alwasy false.

 

[case.learning]

I'm a C++ novice. I'm trying to learn recursion and have written this
piece of code but it doesn't work. Could you help me to see where it
goes wrong? Thanks.

bool PalindromeHelper(string s)
{
int len = s.length();
if (len == 1 || len == 0)
return true;
else
return (s[0] == s[len-1]) &&
PalindromeHelper(s.substr(1, len-2));
}

If the first char is not equal to the last char you sould return
immediately. Once false, alwasy false.

Thanks, but this piece of code that you quoted here actually worked.
The other one didn't work though.

Mark.

 

[Markus Schoder]

I'm a C++ novice. I'm trying to learn recursion and have written this
piece of code but it doesn't work. Could you help me to see where it
goes wrong? Thanks.

bool PalindromeHelper(string s)
{
int len = s.length();
if (len == 1 || len == 0)
return true;
else
return (s[0] == s[len-1]) &&
PalindromeHelper(s.substr(1, len-2)); }

If the first char is not equal to the last char you sould return
immediately. Once false, alwasy false.

It does thanks to the short circuit behaviour of &&.