[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;
    }
}