LeetCode 125 Valid Palindrome

最新推荐文章于 2020-05-27 12:11:01 发布

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本文介绍了一个算法用于判断给定字符串是否为回文串，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.

public class Solution {
    public boolean isPalindrome(String s) {
    	int tmp ='A'-'a';
    	int i=0;
    	int j=s.length()-1;
    	while(i<=j){
    		while(i<s.length()){
        		if('a'<=s.charAt(i)&&s.charAt(i)<='z') break;
        		else if('A'<=s.charAt(i)&&s.charAt(i)<='Z') break;
        		else if('0'<=s.charAt(i)&&s.charAt(i)<='9') break;
        		else i++;
    		}
    		while(0<=j){
        		if('a'<=s.charAt(j)&&s.charAt(j)<='z') break;
        		else if('A'<=s.charAt(j)&&s.charAt(j)<='Z') break;
        		else if('0'<=s.charAt(j)&&s.charAt(j)<='9') break;
        		else j--;
    		}
    		if(i==s.length()) return true;
    		if(s.charAt(i)==s.charAt(j)){
    			i++;
    			j--;
    		}
    		else if(tmp+s.charAt(i)==s.charAt(j)){
    			i++;
    			j--;
    		}
    		else if(s.charAt(i)-tmp==s.charAt(j)){
    			i++;
    			j--;
    		}
    		else return false; 
    	}
        return true;
    }
}