题解 | #密码验证合格程序#

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        while (in.hasNext()) { // 注意 while 处理多个 case
            String code = in.next();

//first , we determin the length,then we go the substring part, last, we determin if there have enough type of characters.
            if (code.length() <= 8) {

                System.out.println("NG");
                
            } else if (!subStringChecker(code)) {
                System.out.println("NG");
                
            } else if (!codeChecker(code)) {
                System.out.println("NG");
                
            }else{
                System.out.println("OK");
			}
        }
    }
    //判断字符数量格式是否符合要求。
    public static boolean codeChecker(String part) {
	  //We use hashset to stroe the characters that have appreared,because it helps us automaticlly repove duplicates.
        HashSet<String> checker = new HashSet<>();
        for (int i = 0; i < part.length(); i++) {
            if (Character.isDigit(part.charAt(i))) {
                checker.add("Digit");
            } else if (Character.isLowerCase(part.charAt(i))) {
                checker.add("LowerCase");
            } else if (Character.isUpperCase(part.charAt(i))) {
                checker.add("UpperCase");
            } else {
                checker.add("Other");
            }

        }
        return checker.size() >= 3;
    }
//we use sliding window to determin if there are repeated sustrings.
    public static boolean subStringChecker(String part) {
        for (int i = 0; i < part.length() - 2; i++) {
//Be careful, in the code snipped"substring(i,i+n)",the index of i+n is exclude, which means that the substring's elements will be part[i],part[i+1] and part[i+2].
            int indicator =  part.indexOf(part.substring(i, i + 3), i + 1);
            if (indicator != -1) {
                return false;
            }
        }
        return true;

    }
}