LeetCode 125. Valid Palindorme (验证回文字符串)

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"

"race a car"

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.

题目标签：String， Two Pointers

　　题目给了我们一个string s， 让我们判断它是不是 palindorme。

　　对于s， 我们只需要比较 字母 和 数字。

       设置一个 left = 0， right = s.length() -1，依次比较，其中遇到任何其他 char 就跳过，具体看code。

　　一开始不知道有 Character.isLetterOrDigit() ，还分别用了 letter 和 digit - -

Java Solution:

Runtime beats 80.01% 

完成日期：03/07/2017

关键词：two pointers

关键点：skip all non-alphanumeric chars

class Solution
{
public boolean isPalindrome(String s)
{
// use two pointers
int left = 0;
int right = s.length() - 1;

char [] char_arr = s.toCharArray();

while(left < right)
{
while(left < right && !Character.isLetterOrDigit(char_arr[left])) // if char is not letter or digit
left++;

while(left < right && !Character.isLetterOrDigit(char_arr[right])) // if char is not letter or digit
right--;

if(Character.toUpperCase(char_arr[left]) != Character.toUpperCase(char_arr[right]))
return false;

left++;
right--;
}

return true;
}

}

参考资料：n/a

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