COJ 1081 集训队分组

http://acm.csu.edu.cn/OnlineJudge/problem.php?id=1081

不是太会写拓扑排序，所以再写一遍。

/*Accepted    880 kb    268 ms    C++/    1671 B    2012-07-29 17:08:30*/
#include<cstdio>
#include<cstring>
#include<cstdlib>

const int MAXN = 1 << 10;
const int MAXM = 10010;

int N, K, M, first[MAXN], e, next[MAXM], v[MAXM];
int topo[MAXN], cnt, vis[MAXN];

void addedge(int x, int y)
{
    v[e] = y;
    next[e] = first[x], first[x] = e ++;
}

void ReadGraph()
{
    int i, x, y;
    memset(first, -1, sizeof first);
    e = 0;
    for(i = 0; i < M; i ++)
    {
        scanf("%d%d", &x, &y);
        addedge(x, y);
    }
}

void dfs(int cur)
{
    int i;
    vis[cur] = 1;
    for(i = first[cur]; i != -1; i = next[i])
        if(!vis[v[i]])
            dfs(v[i]);
    topo[cnt --] = cur;
}

void toposort()
{
    int i;
    cnt = N;
    memset(vis, 0, sizeof vis);
    for(i = 1; i <= N; i ++)
        if(!vis[i])
            dfs(i);
}

void Search(int cur)
{
    int i;
    vis[cur] = 1;
    for(i = first[cur]; i != -1; i = next[i])
        if(!vis[v[i]])
            Search(v[i]);
}

bool judge()
{
    int i, j;
    for(i = 1; i <= K; i ++)
    {
        memset(vis, 0, sizeof vis);
        Search(topo[i]);
        for(j = K + 1; j <= N; j ++)
            if(!vis[topo[j]])
                return false;
    }
    return true;
}

int main()
{
    while(scanf("%d%d%d", &N, &K, &M) == 3)
    {
        ReadGraph();
        toposort();
        bool ok = judge();
        if(ok)
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}