[LeetCode] 126: Valid Palindrome

[Problem]

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.

[Solution]

class Solution {
public:
bool isPalindrome(string s) {
// Note: The Solution object is instantiated only once and is reused by each test case.
int i = 0, j = s.size()-1;
while(i < j){
if(!isalnum(s[i])){
i++;
}
else if(!isalnum(s[j])){
j--;
}
else if(tolower(s[i]) == tolower(s[j])){
i++;
j--;
}
else{
return false;
}
}
return true;
}
};

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