[leetcode]125.Valid Palindrome

题目

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
Example 2:

Input: "race a car"
Output: false

解法

思路

思路很简单，设立两个指针，i从左往右，j从右往左，如果i和j所指的字符不是数字或字母，则继续往右或往左走，如果i和j所指的都为字母，那么比较i和j所指的字符都转为小写，然后判断是否相等即可。

代码

class Solution {
    public boolean isPalindrome(String s) {
        char[] c = s.toCharArray();
        for(int i = 0, j = c.length - 1; i < j;) {
            if(!Character.isLetterOrDigit(c[i])) i++;
            else if(!Character.isLetterOrDigit(c[j])) j--;
            else if(Character.toLowerCase(c[i++]) != Character.toLowerCase(c[j--]))
                return false;
        }
        return true;
    }
}

知识点总结

小写a到z的ASCII范围为 97到122
大写A到Z的ASCII范围为 65到90