Valid Palindrome

题目原型：

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.

基本思路：

把非数字和字母或者是空格的情况排除即可。

	public boolean isPalindrome(String s)
	{
		if (s == null || s.length() == 0)
			return true;
		for (int i = 0, j = s.length() - 1; i < j;)
		{
			
			char ch1 = s.charAt(i);
			char ch2 = s.charAt(j);
			//假如所得字符不在A-Z并且不在a-z也不在0-9或者为空
			while(!(ch1>=‘A‘&&ch1<=‘Z‘)&&!(ch1>=‘a‘&&ch1<=‘z‘)&&!(ch1>=‘0‘&&ch1<=‘9‘)||ch1==‘ ‘)
			{
				i++;
				if(i<j)
					ch1 = s.charAt(i);
				else
					return true;
			}
			while(!(ch2>=‘A‘&&ch2<=‘Z‘)&&!(ch2>=‘a‘&&ch2<=‘z‘)&&!(ch2>=‘0‘&&ch2<=‘9‘)||ch2==‘ ‘)
			{
				j--;
				if(i<j)
					ch2 = s.charAt(j);
				else
					return true;
			}
			//比较时忽略大小写
			String s1 = s.substring(i,i+1);
			String s2 = s.substring(j,j+1);
			if(!s1.equalsIgnoreCase(s2))
				return false;
			else
			{
				i++;
				j--;
			}
		}
		return true;
	}

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Valid Palindrome

原文：http://blog.csdn.net/cow__sky/article/details/21818403