leetcode_question_125 Valid Palindrome

 

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

 

bool ischar(char & ch)

    {

        if('a' <= ch && ch <= 'z') return true;

        else if('0' <= ch && ch <= '9') return true;

        else if('A' <= ch && ch <= 'Z'){ ch += 32; return true; }

        else return false;

    }

    

    bool isPalindrome(string s) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

    	int length = s.length();

        if(length <= 1)return true;

        

		int begin = 0;

		int end = length-1;

		while(begin < end)

		{

			while(begin < end && !ischar(s[begin])) 

				++begin;

			while(begin < end && !ischar(s[end])) 

				--end;

	

			if(s[begin++] != s[end--]) return false;

		}

		return true;

    }