[leetcode]125. Valid Palindrome判断回文串

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

题目

判断回文串，只检查字母，不分大小写。

思路

双指针

代码

 class Solution {
     public boolean isPalindrome(String s) {
         s = s.toLowerCase();
         int left = 0;
         int right = s.length()-1;
         while(left < right){
             // check white spaces
             if(!Character.isLetterOrDigit(s.charAt(left))) left++;
             // check white spaces
             else if(!Character.isLetterOrDigit(s.charAt(right))) right--;
             else if(s.charAt(left) != (s.charAt(right))) return false;
             else {
                 left++ ;
                 right--;
                  }
         }
         return true;
     }
 }