Valid Palindrome
描述
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.
分析
无
代码
// Valid Palindrome
// 时间复杂度O(n)，空间复杂度O(1)
class Solution {
public:
bool isPalindrome(string s) {
transform(s.begin(), s.end(), s.begin(), ::tolower);
auto left = s.begin(), right = prev(s.end());
while (left < right) {
if (!::isalnum(*left)) ++left;
else if (!::isalnum(*right)) --right;
else if (*left != *right) return false;
else { left++, right--; }
}
return true;
}
};