15算法课程 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.

solution:

循环遍历字符串，将非字母非数字的字符用''直接替换掉得到纯字母数字字符串，然后忽略大小写lower()或者upper()判断是否为回文

code:

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