Leetcode 125 Valid Palindrome

pessis1

于 2017-06-15 18:08:55 发布

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分类专栏： Leetcode Double Pointers

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本文介绍了一种使用双指针技术来判断字符串是否为回文的方法，重点在于只考虑字母数字字符并忽略大小写。

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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.

双指针。

傻呵呵的。Character的method拿着用啊。

public class Solution {
    public boolean isPalindrome(String s) {
        if(s == null){
            return false;
        }
        int low = 0;
        int high = s.length() - 1;
        while(low < high){
            if(!Character.isLetterOrDigit(s.charAt(low))){
                low++;
                continue;
            }
            
            if(!Character.isLetterOrDigit(s.charAt(high))){
                high--;
                continue;
            }
            
            if((Character.toLowerCase(s.charAt(low)) != Character.toLowerCase(s.charAt(high)))){
                return false;
            }
            
            low++;
            high--;
        }
        return true;
    }
}