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.
题意：判断给定的字符串是否为回文。回文，亦称回环，是正读反读都能读通的句子，亦有将文字排列成圆圈者。
思路：通过从前后两个方向来判断是否为回文。本题中有效的字符是字母和数字，并且忽略字母的大小写。
代码：
public class Solution { //判断是否为小写、大写、数字 public boolean isalpha(char c){ if(‘a‘ <= c && c <= ‘z‘) return true; if(‘A‘ <= c && c <= ‘Z‘) return true; if(‘0‘ <= c && c <= ‘9‘) return true; return false; } //将大写转换为小写 public char tolower(char c){ if ((c>=‘A‘&&c<=‘Z‘)){ return c = (char) (c-‘A‘ + ‘a‘); } return c; } public boolean isPalindrome(String s) { int n = s.length(); int i = 0,j= n - 1; while(i<j){ if(!isalpha(s.charAt(i))){ i++; continue; } if(!isalpha(s.charAt(j))){ j--; continue; } if(tolower(s.charAt(i))!=tolower(s.charAt(j))) return false; ++i;--j; } return true; } }
结果：
LeetCode(125):Valid Palindrome
原文：http://www.cnblogs.com/Lewisr/p/5111598.html