[leetcode] Valid Palindrome

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.

https://oj.leetcode.com/problems/valid-palindrome/

 

思路：判断palindrome，双指针从两头向内判断即可。注意过滤掉其他字符。

 

public class Solution {

    public boolean isPalindrome(String s) {
        if (s == null || s.length() == 0)
            return true;
        int i = 0;
        int j = s.length() - 1;
        while (i <= j) {
            while (i < s.length() && (!Character.isLetter(s.charAt(i)) && !Character.isDigit(s.charAt(i))))
                i++;
            while (j >= 0 && (!Character.isLetter(s.charAt(j)) && !Character.isDigit(s.charAt(j))))
                j--;
            if (i > j)
                break;
            if (Character.toUpperCase(s.charAt(i)) != Character.toUpperCase(s.charAt(j)))
                return false;
            i++;
            j--;
        }
        return true;
    }

    public static void main(String[] args) {
        System.out.println(new Solution().isPalindrome("abcaa"));
    }

}

 

第二遍记录：

注意终止条件和过滤其他字符。