Leetcode051--判斷迴文數（忽律大小寫和非字符）

一、原題

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.

二、中文

判斷字符串是否是迴文數，除去我們所有的非字符因素和大小寫

三、舉例

"A man, a plan, a canal: Panama"是迴文數
"race a car" 不是迴文數

四、思路

其實就是將所有的不是的的因素除去就可以了，然後用兩個指針來判斷是否是對稱的

五、程序

import java.util.*;
public class Solution {
    public boolean isPalindrome(String s) {
    	if(s == null){
            return false;
        }
        int i = 0;
        int j = s.length() - 1;
        while(i < j){
            if (!isAlphanumeric(s.charAt(i))) {
                i++;
                continue;
            }
            if (!isAlphanumeric(s.charAt(j))) {
                j--;
                continue;
            }
            if(Character.toLowerCase(s.charAt(i)) == Character.toLowerCase(s.charAt(j))){
                i++;
                j--;
                continue;
            }
            return false;
        }
        return true;
    }
   
    //判斷是否是字符或者數字
    public boolean isAlphanumeric(char c) {
        if ((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9')) {
            return true;
        }
        return false;
    }
}