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Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.
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.
O(n) time without extra memory.
//// consider the lowercase
public class Solution { /** * @param s A string * @return Whether the string is a valid palindrome */ public boolean isPalindrome(String s) { // Write your code here if(s==null || s.length()==0) return true; s=s.toLowerCase(); char[] c=s.toCharArray(); int len=s.length(); int left=0; int right=len-1; while(left<right) { if(!isValid(c[left])) { left++; } if(!isValid(c[right])) { right--; } if(c[left]!=c[right] && left<right) { return false; } else { left++; right--; } } return true; } public boolean isValid(char c) { if(c<=‘z‘&&c>=‘a‘) return true; if(c>=‘0‘&&c<=‘9‘) return true; return false; } }
[lintcode easy]Valid Palindrome
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原文地址：http://www.cnblogs.com/kittyamin/p/5011833.html
