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Question：
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.
1、题型分类：
2、思路：采用双指针，一个从前一个从后。
3、时间复杂度：
4、代码：
public boolean isPalindrome(String s) { if(s.length()<=1) return true; int begin=0,end=s.length()-1; while(begin<=end) { char b=s.charAt(begin); char e=s.charAt(end); if(!isCharacterNummeric(b)) { begin++; continue; } if(!isCharacterNummeric(e)) { end--; continue; } if(intoLowwerCase(b)!=intoLowwerCase(e)) return false; else { begin++;end--;} } return true; } public boolean isCharacterNummeric(char c) { return (c>=‘a‘ && c<=‘z‘) || (c>=‘A‘ && c<=‘Z‘) || (c>=‘0‘ && c<=‘9‘); } public char intoLowwerCase(char c) { if(c>=‘a‘ && c<=‘z‘) return (char)(c-32); return c; }
5、优化：
6、扩展：
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原文地址：http://www.cnblogs.com/maydow/p/4644575.html
