125.Valid-Palindrome

125. Valid Palindrome

题目地址

题目描述

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
Input: "A man, a plan, a canal: Panama"
Output: true
Example 2:
Input: "race a car"
Output: false

代码

public class Solution {
public boolean isPalindrome(String s) {
// 1. input validation
if (s == null || s.trim().isEmpty()) return true;
// 2. Filter punctuation character
int l = 0;
int r = s.length() - 1;
while (l < r) {
// 先过滤
if (!Character.isLetterOrDigit(s.charAt(l))) {
l++;
continue;
}
if (!Character.isLetterOrDigit(s.charAt(r))) {
r--;
continue;
}
// 判断 left 和 right
if (Character.toLowerCase(s.charAt(l)) == Character.toLowerCase(s.charAt(r))) {
l++;
r--;
} else {
return false;
}
}
return true;
}
}