问题描述

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.

class Solution {
public:
	bool isPalindrome( string s ) {
		if( s == "" ) {
			return true;
		}
        
		string allAlphanumeric;
		for( int i = 0; i != s.size(); ++i ) {
			if( isalnum( s[i] ) ) {
				allAlphanumeric.push_back( tolower( s[i] ) );
			}
		}
		if( allAlphanumeric.size() == 1 ) {
			return true;
		}

		bool result = true;
		unsigned size = allAlphanumeric.size();
		for( int i = 0; i < size / 2; ++i ) {
			if( allAlphanumeric[i] != allAlphanumeric[size - i - 1] ) {
				result = false;
				break;
			}
		}
		return result;
	}
};

Valid Palindrome