LeetCode - 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.

Solution:

 1 public class Solution {
 2     public boolean isValid(char c){
 3         if(c >= 'a' && c <= 'z') return true;
 4         if(c >= '0' && c <= '9') return true;
 5         return false;
 6     }
 7     public boolean isPalindrome(String s) {
 8         // Start typing your Java solution below
 9         // DO NOT write main() function
10         if(s.equals("")) return true;
11         s = s.toLowerCase();
12         int len = s.length();
13         int left = 0, right = len - 1;
14         while(left < right){
15             while(!isValid(s.charAt(left))){
16                 left++;
17                 if(left >= right) return true;
18             } 
19             while(!isValid(s.charAt(right))){
20                 right--;
21                 if(left >= right) return true;
22             }
23             if(s.charAt(left) != s.charAt(right)) return false;
24             left++;
25             right--;
26         }
27         return true;
28     }
29 }

 

More strictly, 

 1 public class Solution {
 2     public boolean isPalindrome(String s) {
 3         // Start typing your Java solution below
 4         // DO NOT write main() function
 5         if(s.equals("")) return true;
 6         int len = s.length();
 7         for(int i = 0; i <= len / 2; i++) {
 8             if(s.charAt(i) != s.charAt(len - 1 - i))
 9                 return false;
10         }
11         return true;
12     }
13 }

 

 

转载于:https://www.cnblogs.com/cheapcrook/archive/2013/01/25/2876742.html