拓撲排序

#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;
const int N = 1e5 + 10 ;
int deg[N], ne[N], e[N], h[N];
int n, len, m, a[N], cnt = 1;

void add(int a, int b)
{
	e[len] = b;
	ne[len] = h[a];
	h[a] = len++;
}

void topsort()
{
	queue<int> q;
	for (int i = 1; i <= n; i++)
		if (deg[i] == 0)
		{
			q.push(i);
			break;
		}
	while (q.size())
	{
		int x = q.front();
		q.pop();
		a[cnt++] = x;
		for (int i = h[x]; ~i; i = ne[i])
		{
			int y = e[i];
			if (--deg[y] == 0)
				q.push(y);
		}
	}
}

int main()
{
	scanf("%d%d", &n, &m);
	memset(h, -1, sizeof h);
	for (int i = 1; i <= m; i++)
	{
		int x, y;
		scanf("%d%d", &x, &y);
		add(x, y);
		deg[y]++;
	}
	topsort();
	if(a[n] == 0)
	{
	    cout << -1 << endl;
	    return 0;
	}
	for (int i = 1; i <= n; i++)
		cout << a[i] << " ";
	cout << endl;
	return 0;
}