leecode 回文字符串加强版

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.

只考虑数字和字母，字母大小写都一样，判断是否是回文。重点是忽略非非字母和数字。比较简单。

 1 public class Solution {
 2     public boolean isPalindrome(String s) {
 3
 4         int low=0;
 5         int high=s.length()-1;
 6         String s1=s.toLowerCase();
 7         while(low<high)
 8         {
 9
10             while(low<high)
11             {
12                char c=s1.charAt(low);
13                if((c>=‘a‘&&c<=‘z‘)||(c>=‘0‘&&c<=‘9‘))
14                {
15                    break;
16                }
17                else  low++;
18
19             }
20
21              while(low<high)
22             {
23                char c=s1.charAt(high);
24                if((c>=‘a‘&&c<=‘z‘)||(c>=‘0‘&&c<=‘9‘))
25                {
26                    break;
27                }else high--;
28
29             }
30
31
32
33             if(s1.charAt(low)==s1.charAt(high))
34             {
35                 low++;
36                 high--;
37             }
38             else
39             {
40                 return false;
41             }
42
43
44
45         }
46
47         return true;
48
49
50     }
51 }

leecode 回文字符串加强版