[LeetCode] Valid Palindrome

最新推荐文章于 2019-11-04 14:27:48 发布

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最新推荐文章于 2019-11-04 14:27:48 发布

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分类专栏： leetcode 文章标签： java leetcode

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本文介绍了一个简单的算法，用于判断一个字符串是否为回文，重点在于只考虑字母和数字字符，并忽略大小写。通过双指针法，从字符串两端向中间遍历比较字符，实现了高效的回文判断。

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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

题目比较简单，注意别把数字排除。判断是否相等是记得统一大小写，有个非常好用的方法 Character.toLowerCase(char)

public class Solution {
    public boolean isPalindrome(String s) {
        if (s == null) {
            return false;
        }
        
        if (s.length() < 1) {
            return true;
        }
        
        int i = 0;
        int j = s.length() - 1;
        
        while (i < j) {
            char left = s.charAt(i);
            char right = s.charAt(j);
            
            if (!((left >= 'a' && left <= 'z') || (left >= 'A' && left <='Z') || (left >= '0' && left <='9'))) {
                i++;
                continue;
            }
            
            if (!((right >= 'a' && right <= 'z') || (right >= 'A' && right <='Z') || (right >= '0' && right <='9'))) {
                j--;
                continue;
            }
            
            if (Character.toLowerCase(left) != Character.toLowerCase(right)) {
                return false;
            }
            i++;
            j--;
        }
        
        return true;
    }
}