用c++STL queue的解法

#include<iostream>
#include<algorithm>
#include<queue>
#include<vector>
#include<cstring>
using namespace std;

const int N = 1e5 + 10;
int e[N], ne[N], h[N], idx, d[N];
int n, m;

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

bool topsort()
{
    vector<int>result;
    //初始化队列
    queue<int>q;
    for (int i = 1; i <= n; i++)
        if (d[i] == 0)
            q.push(i);
    while (!q.empty())
    {
        int t = q.front();
        q.pop();
        result.push_back(t);

        for (int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (--d[j] == 0)
            {
                q.push(j);
            }
        }
    }
    if (result.size() != n)return false;
    for (auto x : result)
    {
        printf("%d ", x);
    }
    cout << endl;
    return true;
}

int main()
{
    memset(h, -1, sizeof h);
    cin >> n >> m;
    while (m--)
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
        d[b]++;
    }
    if (!topsort())cout << "-1" << endl;
    return 0;
}