题解 | #幼儿园分班#

import java.util.*;

public class Main{

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int stu_num = sc.nextInt(); sc.nextLine();
        int pro_num = sc.nextInt(); sc.nextLine();
        HashSet<Integer> leftMap = new HashSet<Integer>();
        HashSet<Integer> rightMap = new HashSet<Integer>();
        boolean flag = true;
        for(int i=1;i<=pro_num;i++){
            int left = sc.nextInt();
            int right = sc.nextInt();
            if((leftMap.contains(left)&&leftMap.contains(right))||(rightMap.contains(left)&&rightMap.contains(right))){
                flag = false;
                break;
            }
            if(leftMap.contains(left)){
                rightMap.add(right);
                sc.nextLine();
                continue;
            }
            if (rightMap.contains(left)){
                leftMap.add(right);
                sc.nextLine();
                continue;
            }
            if(leftMap.contains(right)){
                rightMap.add(left);
                sc.nextLine();
                continue;
            }
            if (rightMap.contains(right)){
                leftMap.add(left);
                sc.nextLine();
                continue;
            }
            leftMap.add(left);
            rightMap.add(right);
            sc.nextLine();
        }
        if (flag){
            System.out.println(1);
        }else {
            System.out.println(0);
        }
    }

}