中秋节弱校的一场小比赛的第二题。。SYZOJ 这是第二题，典型的拓扑排序，只是需要添加一个优先队列来保证输出满足字典序。 题比较水，直接贴代码了。

#include 
#include 
#include 
#include 
using namespace std;
const int MX = 1e5 + 5;
int n, m, head[MX], tot, cnt, in[MX];
int ans[MX];
bool vis[MX];
struct edge{
    int fr, to, ne;
}e[1000005];
priority_queue<int, vector, greater > q;
void addedge(int a, int b) {
    tot++;
    e[tot].fr = a;
    e[tot].to = b;
    e[tot].ne = head[a];
    head[a] = tot;
}
void bfs() {
    for (int i = 1; i <= n; i++) {
        if (!in[i]) {
            q.push(i);
        }
    }
    while (!q.empty()) {
        int now = q.top();
        ans[++cnt] = now;
        q.pop();
        for (int i = head[now]; i; i = e[i].ne) {
            int to = e[i].to;
            if (vis[to]) continue;
            in[to]--;
            if (in[to] != 0) continue;
            vis[to] = true;
            q.push(to);
        }
    }
    if (cnt == n) {
        for (int i = 1; i <= n; i++) {
            printf("%d ", ans[i]);
        }
        printf("\n");
    } else {
        printf("-1\n");
    }
}
int main() {
    scanf("%d%d", &n, &m);
    int x, y;
    for (int i = 1; i <= m; i++) {
        scanf("%d%d", &x, &y);
        in[y]++;
        addedge(x, y);
    }
    bfs();
    return 0;
}