Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.//数字或字母

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.

思路：使用string中erase函数剔除非数字、字母，在判定是否符合条件

        注意++i的位置，erase(i,1)后，应继续从i位置检查，而不应该++i；

        erase()函数用法

code：

class Solution {
public:
    bool isPalindrome(string s) {
        
        for(int i=0;i<s.size();)
        {
            if(!(s[i]>='a'&&s[i]<='z'||s[i]>='0'&&s[i]<='9'))
                s.erase(i,1);
            else
                ++i;
        }
        
        for(int i=0,j=s.size()-1;(i<s.size()-1)&&(j>=0);++i,--j)
        {
            if(!(s[i]==s[j]||abs(s[i]-s[j])==32))
                return false;
        }
        
        return true;
    }
};