杭电ACM1285----确定比赛名次『拓扑排序』

//裸拓扑排序，注意先输出比较小的数，使用优先队列即可
#include <cstdio>
#include <vector>
#include <cstring>
#include <queue>
#include <algorithm>
using namespace std;
const int maxn = 505;
vector<int> v[maxn];
priority_queue<int> q;
int f[maxn];
int main()
{
    int n,m,x,y;
    while(~scanf("%d%d",&n,&m))
    {
        memset(f,0,sizeof f);
        for(int i = 1; i <= n; ++i)
            v[i].clear();
        while(m--)
        {
            scanf("%d%d",&x,&y);
            v[x].push_back(y);
            ++f[y];
        }
        for(int i = 1; i <= n; ++i)
            if(f[i] == 0)
                q.push(-i);//默认大根堆
        bool flag = true;
        while(!q.empty())
        {
            int t = -q.top(); q.pop();
            if(flag) { printf("%d",t); flag = false;}
            else printf(" %d",t);
            for(int i = 0; i < v[t].size(); ++i)
                if(!(--f[v[t][i]])) q.push(-v[t][i]);
        }
        printf("
");
    }
    return 0;
}