Valid Palindrome LeetCode Java

描述
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? �is is a good question to ask during an
interview.
For the purpose of this problem, we define empty string as valid palindrome.

分析
去标点符号，看是不是回文
代码

public class ValidPalindrome {
    public static void main(String[] args) {
        String str= "A man, a plan, a canal: Panama";
        System.out.println(validPalindrome(str));
    }
    public static boolean validPalindrome(String str) {
        if (str=="") 
            return true;
//        String regex= "/[^\u4e00-\u9fa5\w]/g";
        String regex= "[\p{Punct}\p{Space}]+"; //去标点符号的正则表达式， 但不能去“”和中文标点
        str=str.replaceAll(regex,"");
        String strlow=str.toLowerCase();
//        return strlow;
        char[] ch=strlow.toCharArray();
    
        for(int i=0;i<ch.length;i++) {
            int j=ch.length-1-i;
            if(i<=j) {
               if(ch[i]==ch[j]) {
                   continue;
               }else {
                   return false;
               }
            }
        }
        return true;
    }
}

方法2（转载）

不用正则

public static boolean isPalindrome(String s) {
                      if(s.length()==0)
                          return true;
                      
                      s = s.toUpperCase();
                      int low1 = 'A', high1 = 'Z';
                      int low2 = '0', high2 = '9';
                      int low = 0, high = s.length()-1;
                      
                     while(low < high){
                         if((s.charAt(low)<low1||s.charAt(low)>high1)
                             && (s.charAt(low)<low2||s.charAt(low)>high2)){
                                 low++;
                                 continue;
                             }
                             
                         if((s.charAt(high)<low1||s.charAt(high)>high1)
                             && (s.charAt(high)<low2||s.charAt(high)>high2)){
                                 high--;
                                 continue;
                             }
                         if(s.charAt(low) == s.charAt(high)){
                             low++;
                             high--;
                         }else
                             return false;
                     }
                     return true;
                 }