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一天一道LeetCode

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（一）题目

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.

（二）解题

题目大意：判断一个字符串是不是有效的回文字符串。忽略里面除了数字和字母的其他字符。

直到i>=j时，说明是有效回文，返回true。

//isalnum()是判断该字符是不是字母或数字class Solution {public:    bool isPalindrome(string s) {        int len = s.length();        int i = 0;        int j = len-1;        while(i<=j)        {            while(!isalnum(s[i])&&i<=j) i++;//直到s[i]为字母或数字为止            while(!isalnum(s[j])&&i<=j) j--;//直到s[j]为字母或数字为止            if(i<=j&&tolower(s[i])!=tolower(s[j])) return false;//如果不等就返回false            i++;j--;//反之就继续比较        }        return true;    }};