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
题目中是对数字和字母进行回文判断，而对其他的字符 ! ? . , " ; : @ # % $ * - / 等都是忽略的，所以有个问题，就是要忽略掉这些乱七八糟的东西，而一般的加条件进行判断也不太好用，
看到讨论区有 用Character.isLetterOrDigit(ch)来进行筛选，很厉害了。
class Solution {
public boolean isPalindrome(String s) {
if(s == null || s.length() == 0) return true;
StringBuilder sb = new StringBuilder();
for(int i = 0; i < s.length(); i++){
if(Character.isLetterOrDigit(s.charAt(i))){
sb.append(s.charAt(i));
}
}
String str = sb.toString().toLowerCase();
String res = sb.reverse().toString().toLowerCase();
if(str.equals(res)) return true;
return false;
}
}
那句话可以这样代替，很笨
class Solution {
public boolean isPalindrome(String s) {
if(s == null || s.length() == 0) return true;
StringBuilder sb = new StringBuilder();
for(int i = 0; i < s.length(); i++){
if((s.charAt(i) >= ‘a‘ && s.charAt(i) <= ‘z‘) || (s.charAt(i) >= ‘A‘ && s.charAt(i) <= ‘Z‘) || (s.charAt(i) >= ‘0‘ && s.charAt(i) <= ‘9‘) ){
sb.append(s.charAt(i));
}
}
String str = sb.toString().toLowerCase();
String res = sb.reverse().toString().toLowerCase();
if(str.equals(res)) return true;
return false;
}
}
原文：https://www.cnblogs.com/SkyeAngel/p/9120080.html