Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Notice
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.
Have you met this question in a real interview?
Example
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.
Challenge
O(n) time without extra memory.
LeetCode上的原题，请参见我之前的博客Valid Palindrome。
解法一：
class Solution {
public:
/**
* @param s A string
* @return Whether the string is a valid palindrome
*/
bool isPalindrome(string& s) {
int left = , right = s.size() - ;
while (left < right) {
if (!isAlNum(s[left])) ++left;
else if (!isAlNum(s[right])) --right;
else if ((s[left] + - 'a') % != (s[right] + - 'a') % ) return false;
else {
++left; --right;
}
}
return true;
}
bool isAlNum(char c) {
if (c >= 'a' && c <= 'z') return true;
if (c >= 'A' && c <= 'Z') return true;
if (c >= '' && c <= '') return true;
return false;
}
};
解法二：
class Solution {
public:
/**
* @param s A string
* @return Whether the string is a valid palindrome
*/
bool isPalindrome(string& s) {
int left = , right = s.size() - ;
while (left < right) {
if (!isalnum(s[left])) ++left;
else if (!isalnum(s[right])) --right;
else if ((s[left] + - 'a') % != (s[right] + - 'a') % ) return false;
else {
++left; --right;
}
}
return true;
}
};