LeetCode3.1 @ Valid Palindrome 检验回文串 D2F5

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.

思路：头尾两个指针向中间走，两两比较。因为题目要求跳过标点空格比较，所以要有判断。

public class Solution {
    public boolean isPalindrome(String s) {
        if(s==null || s.length()==0)
            return true;
        int l=0;
        int r=s.length()-1;
        while(l<r){
            if(!isValid(s.charAt(l))){
                l++;
                continue;
            }
            if(!isValid(s.charAt(r))){
                r--;
                continue;
            }
            if(!isSame(s.charAt(l),s.charAt(r))){
                return false;
            }
            l++;
            r--;
        }
        return true;
    }
    private boolean isValid(char c){
        if('a'<=c && c<='z' || 'A'<=c && c<='Z' || '0'<=c && c<='9')
            return true;
        return false;
    }
    private boolean isSame(char c1,char c2){
        if('A'<=c1 && c1<='Z')  
            c1 = (char)(c1-'A'+'a');  
        if('A'<=c2 && c2<='Z')  
            c2 = (char)(c2-'A'+'a');  
        return c1==c2;  
    }
}

【后记】相关题目总结 http://blog.youkuaiyun.com/linhuanmars/article/details/22775045