Leetcode Valid Palindrome

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本文介绍了一种算法，用于判断一个字符串是否为回文，只考虑字母数字字符并忽略大小写。通过双指针技巧实现，从两端向中间扫描，跳过非字母数字字符，将所有字符转换为小写进行比较。

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.

注意题目条件，字符数字字符，忽略大小写需要我们在判断的时候将两个字符都转为小写进行判断。

代码如下：

class Solution {
public:
    bool isPalindrome(string s) {
        int begin=0,end=s.size()-1;
        while(begin < end)
        {
            while(!isalnum(s[begin]))
                begin++;
            while(!isalnum(s[end]))
                end--;
            if(begin<end && tolower(s[begin]) != tolower(s[end]))
                return false;
            begin++;end--;
        }
        return true;
    }
};