拓扑排序 ： 记录入度，入度为0就入队

#include <cstdio>
#include <vector>
#include <iostream>
#include <queue>
using namespace std;

const int N=101;

int n,m,in[N],x,y,ans[N],sum,top;

vector < int > f[N];

queue < int > q;

void inp()
{
    scanf ("%d %d",&n,&m);
    while( cin >> x >> y)
    {
        if( x == 0 && y == 0) break;
        f[x].push_back(y);
        in[y]++;   //入度加一；
    }
}

void work()
{
    for (int i = 1; i <= n; i++)
        if( in[i] == 0) q.push(i);
    while(!q.empty())
    {
        sum = q.front();
        q.pop();
        ans[++top] = sum;
        for (int i = 0; i < f[sum].size(); i++)
        {
            in[f[sum][i]]--;
            if(in[f[sum][i]] == 0) q.push(f[sum][i]);
        }       
    }
}

void putp()
{
    for (int i = 1; i <= n ; i++)
        printf("%d ",ans[i]);
}

int main()
{
    inp();
    work();
    putp();
    return 0;
}