125. Valid Palindrome

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..

先扫一遍忽略空格，塞到char[]里面，从两端检测

public class Solution {   public boolean isPalindrome(String s){int len=s.length();if(len==0)return true;char[] carr=new char[len];int cnt=0;for(int i=0;i<len;i++){char c=s.charAt(i);if(c>='0'&&c<='9'||c>='a'&&c<='z'||c>='A'&&c<='Z')carr[cnt++]=c;}String str=new String(carr, 0, cnt);str=str.toLowerCase();int size=str.length();for(int i=0,j=size-1;i<size;i++,j--)if(str.charAt(i)!=str.charAt(j))return false;return true;}}