LeetCode125——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.

题目大意

给定一个字符串，判断是不是回文，只考虑字母数字字符，并不顾大小写。另外，空串被认为是有效的回文。

难度系数：容易

实现

bool isAlphanumeric(const char c) {    if ('A' <= c && c <= 'Z')        return true;    else if ('a' <= c && c <= 'z')        return true;    else if ('0' <= c && c <= '9')        return true;    return false;}char toLower(const char c){    if ('A' <= c && c <= 'Z')        return 'a' + c - 'A';    return c;}bool isPalindrome(string s){    if (s.empty())        return true;    int begin = 0;    int end = s.size() - 1;    while (true) {        while (begin < s.size() && !isAlphanumeric(s[begin])){            begin++;        }        while (end >= 0 && !isAlphanumeric(s[end])) {            end--;        }        if (end <= begin)            return true;        if (toLower(s[begin]) != toLower(s[end])){            return false;        }        begin++;        end--;    }}