[数据结构与算法]ooj1138C语言合法标识符

import java.util.Scanner;

public class oj1 {
    public static void main(String[] args){
        Scanner input = new Scanner(System.in);
        String s = input.nextLine();
        char[] chars = s.toCharArray();
        int k = 0;
        if(Judge(chars[0]) != 1){
            System.out.println("no");
        }else {
            for (char c : chars) {
                if(Judge(c) == 0){
                    System.out.println("no");
                    k=1;
                    break;
                }
            }
            if(k==0) System.out.println("yes");
        }
    }

    private static int Judge(char c) {
        if(c<='9' && c>='0' || c<='z' && c>='a' || c<='Z' && c>='A' || c == '_'){
            if (c<='9' && c>='0'){
                return 2;  //判断第一个字符是否为数字
            }else {
                return 1; //第一个字符为字母或下划线
            }
        }else {
            return 0;
        }
    }
}