題目：

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.

解題思路：

設(shè)置前后兩個指針，依次比較，若不相等則表明不是回文串。注意調(diào)過不是字母的字符。

代碼：

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

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轉(zhuǎn)載于:https://www.cnblogs.com/dongguangqing/p/3727758.html

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