Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example 1:
Input: "A man, a plan, a canal: Panama"
Output: true
Example 2:
Input: "race a car"
Output: false
1 char c = 'x' ,判断c:
if ((a >= '0' && a <= '9') || (a >= 'a' && a <= 'z') || (a >= 'A' && a <= 'Z')) {
return true;
}
2 转为字符串
String.valueO