leetcode- 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.

bool isPalindrome(char* s) {
    //s=strupr(s);
    int i=0,j=strlen(s)-1,k=j+1;
    while(i<j){
        while((!((s[i]>='A'&&s[i]<='Z')||(s[i]>='a'&&s[i]<='z')||(s[i]>='0'&&s[i]<='9'))) &&i<k){
            i++;
        }
        while((!((s[j]>='A'&&s[j]<='Z')||(s[j]>='a'&&s[j]<='z')||(s[j]>='0'&&s[j]<='9'))) &&j>0){
            j--;
        }
        //printf("%d%d,%d,%d",i,j,abs(s[i]-s[j]),'a'-'A');
        if( i<=j&&
            (s[i]!=s[j] )&&
            !(
            ((s[j]>='A'&& s[j]<='Z') || (s[j]>='a' && s[j]<='z'))&&
            ((s[i]>='A'&& s[i]<='Z') || (s[i]>='a' && s[i]<='z'))&& 
            (abs(s[i]-s[j])==('a'-'A')))
          ) return false;
        i++;j--;
    }
    return true;
}