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.

题意：判断一个string句子是否回文。

思路：读懂题意，然后从两端开始检测。

class Solution {public:bool isPalindrome(string s) {int i = 0;int j = s.size() - 1;while (i < j){if (!((s[i] >= 48 && s[i] <= 57) || (s[i] >= 65 && s[i] <= 90) || (s[i] >= 97 && s[i] <= 122))){i++;continue;}if (!((s[j] >= 48 && s[j] <= 57) || (s[j] >= 65 && s[j] <= 90) || (s[j] >= 97 && s[j] <= 122))){j--;continue;}if (s[i] == s[j] || (s[i] >= 65 && s[j] >= 65 && (s[i] - s[j] == 32 || s[i] - s[j] == -32))){i++;j--;}else{return false;}}return true;}};