java 代码

import java.io.*;
import java.lang.*;
import java.util.*;
class Main{
    static int n = 0, m = 0, N = 100010;
    static int[] h = new int[N];//邻接表数组
    static int[] e = new int[N], ne = new int[N];//单链表
    static int idx = 1;
    static int[] q = new int[N], out = new int[N], in = new int[N];
    static void add(int a, int b){
        e[idx] = b; ne[idx] = h[a]; h[a] = idx++;
        out[a]++;//初度+1
        in[b]++;//入度+1
    }

    static boolean sort(){
        int hh = 0, tt = -1;
        for(int i = 1; i <= n; ++i){//所有入度为0的先进入队列
            if(in[i] == 0){
                q[++tt] = i;
            }
        }
        while(hh <= tt){
            int t = q[hh++];
            for(int i = h[t]; i != -1; i = ne[i]){
                int j = e[i];
                if(in[j]  != 0){
                    in[j]--;
                    out[t]--;
                }
                if(in[j] == 0){
                    q[++tt] = j;
                }
            }
        }
        return tt == n - 1;
    }

    public static void main(String[] args)throws Exception{
        BufferedReader buf = new BufferedReader(new InputStreamReader(System.in));
        String[] params = buf.readLine().split(" ");
        n = Integer.valueOf(params[0]);
        m = Integer.valueOf(params[1]);
        Arrays.fill(h, -1);
        for(int i = 1; i <= m; ++i){
            String[] info = buf.readLine().split(" ");
            int a = Integer.valueOf(info[0]);
            int b = Integer.valueOf(info[1]);
            add(a, b);//有向图
        }
        int t = 0;
        if(sort()){
            while(n-- != 0){
                System.out.print(q[t++] + " ");
            }
        }else{
            System.out.print(-1);
        }
    }
}