PU 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.

C Solution:

bool isPalindrome(char* s) {
    char *t = s + strlen(s) - 1;
    char flag[256] = {0};
    int i;
    for (i = 0; i < 10; i++) flag['0' + i] = '0' + i;
    for (i = 0; i < 26; i++) flag['a' + i] = flag['A' + i] = 'a' + i;
    while (s < t) {
        while (s < t && !flag[*s]) s++;
        if (s == t) return true;
        while (!flag[*t]) t--;
        if (flag[*s++] != flag[*t--]) return false;
    }
    return true;
}

Summary:

• nothing to say

LeetCode: 125. Valid Palindrome