[LeetCode] 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"isnota 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.

解题思路：

题意为不区分大小写，且只判断数字和字母。有个transform函数学会了：std::transform(s.begin(), s.end(), s.begin(), ::tolower);，能够将字符串转化成小写形式。

class Solution {public:bool isPalindrome(string s) {int len = s.length();std::transform(s.begin(), s.end(), s.begin(), ::tolower); //这个函数学会int i=0, j=len-1;while(i<j){if(!isAlphanumeric(s[i])){i++;continue;}if(!isAlphanumeric(s[j])){j–;continue;}if(s[i]!=s[j]){return false;}i++;j–;}return true;}private:bool isAlphanumeric(char c){if(c>='a'&&c<='z' || c>='0'&&c<='9'){return true;}return false;}};

，第一个青春是上帝给的;第二个的青春是靠自己努力的