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 }