LeetCode: Valid Palindrome 解题报告

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:

左右指针往中间判断。注意函数： toLowerCase

 /*
     SOLUTION 1: Iterator.
     */
     public boolean isPalindrome1(String s) {
         if (s == null) {
             return false;
         }

         int len = s.length();

         boolean ret = true;

         int left = 0;
         int right = len - 1;

         String sNew = s.toLowerCase();

         while (left < right) {
             // bug 1: forget a )
             while (left < right && !isNumChar(sNew.charAt(left))) {
                 left++;
             }

             while (left < right && !isNumChar(sNew.charAt(right))) {
                 right--;
             }

             if (sNew.charAt(left) != sNew.charAt(right)) {
                 return false;
             }

             left++;
             right--;
         }

         return true;
     }

     public boolean isNumChar(char c) {
         if (c <= '9' && c >= '0' || c <= 'z' && c >= 'a' || c <= 'Z' && c >= 'A') {
             return true;
         }

         return false;
     }

SOLUTION 2:

引自http://blog.csdn.net/fightforyourdream/article/details/12860445 的解答，会简单一点儿。不用判断边界。

左右指针往中间判断。新技能GET: isLetterOrDigit

 /*
     SOLUTION 2: Iterator2.
     */
     public boolean isPalindrome(String s) {
         if (s == null) {
             return false;
         }

         int len = s.length();

         boolean ret = true;

         int left = 0;
         int right = len - 1;

         String sNew = s.toLowerCase();

         while (left < right) {
             // bug 1: forget a )
             if (!Character.isLetterOrDigit(sNew.charAt(left))) {
                 left++;
             // bug 2: Line 67: error: cannot find symbol: method isLetterOrDigital(char)
             } else if (!Character.isLetterOrDigit(sNew.charAt(right))) {
                 right--;
             } else if (sNew.charAt(left) != sNew.charAt(right)) {
                 return false;
             } else {
                 left++;
                 right--;
             }
         }

         return true;
     }

GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/string/IsPalindrome_2014_1229.java