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.
一刷
题解：思路很简单，但是有很多细节需要注意
- 字母和数字都是有效的， 且a和A相等。所以要统一转为up或low case然后再用相等条件。
- 注意在lo++, hi--的时候不能超出边界所以.charAt之前要边界判断。
- 注意存在函数Character.isLetterOrDigit
public class Solution {
public boolean isPalindrome(String s) {
int lo = 0, hi = s.length()-1;
while(lo<hi){
while(inValid(s, lo) && lo<hi) lo++;
while(inValid(s, hi) && lo<hi) hi--;
if(Character.toUpperCase(s.charAt(lo))!=Character.toUpperCase(s.charAt(hi))) return false;
lo++;
hi--;
}
return true;
}
private boolean inValid(String s, int index){
char ch = s.charAt(index);
if(!Character.isDigit(ch) && !Character.isAlphabetic(ch)) return true;
else return false;
}
}
二刷
two pointer
