验证回文串

https://leetcode-cn.com/explore/featured/card/top-interview-questions-easy/5/strings/36/

class Solution {
     public boolean isPalindrome(String s) {
        int sum = 0;
        char[] chars = s.toCharArray();
        char[] arr = new char[chars.length];
        for (int i = 0; i < chars.length; i++){
            if (check(chars, i)){
                arr[sum++] = chars[i];
            }
        }
        for (int i = 0; i < sum / 2; i++){
            if (arr[i] != arr[sum - i -1]){
                return false;
            }
        }

        return true;
    }


    private boolean check(char[] ch, int i){

        if (ch[i] <= 'Z' && ch[i] >= 'A'){
            ch[i] += 32;
            return true;
        }
        if (ch[i] >= 'a' && ch[i] <= 'z'){
            return true;
        }
        if (ch[i] <= '9' && ch[i] >= '0' ){
            return true;
        }
        return false;
    }

}