hdu 1181

并查集 + 拓扑排序。

拓扑排序具体怎么用还要学习，这个题里面就是从入度为零开始算起。一次只有一个入度为零，若大于一，则UNCERTAIN 如果执行完毕，还有数字没被计算，那么有环，则CONFLICT；

#include<cstdio>
#include<vector>
#include<cstring>
#include<queue>
using namespace std;
const int maxn = 10000 + 5;
struct node
{
    int a,b;
    char op;
} ship[maxn];
int pre[maxn];
vector<int> u[maxn];
int in[maxn];
int n, m, sum;
void init()
{
    sum = n;
    for(int i = 0; i <= n; i++)
        u[i].clear();
    for(int i = 0; i <= n; i++)
        pre[i] = i;
    memset(in, 0, sizeof(in));
}
int root(int x)
{
    if(x != pre[x])
        pre[x] = root(pre[x]);
    return pre[x];
}
int merge_set(int x, int y)
{
    int fx = root(x);
    int fy = root(y);
    if(fx == fy) return false;
    else
    {
        pre[fx] = fy;
        return true;
    }
}
void top_sort()
{
    int little = false;
    queue<int> q;
    for(int i = 0; i < n; i++)
    {
        if(pre[i] == i && !in[i])
            q.push(i);
    }
    while(!q.empty())
    {
        if(q.size() > 1) little = true;
        int t = q.front();
        sum--;
        q.pop();
        for(int i = 0; i < u[t].size(); i++)
        {
            in[u[t][i]]--;
            if(in[u[t][i]] == 0)
            {
                q.push(u[t][i]);
            }
        }
    }
    if(sum > 0) printf("CONFLICT\n");
    else if(little) printf("UNCERTAIN\n");
    else printf("OK\n");
}
int main()
{
    while(scanf("%d%d", &n, &m) == 2)
    {
        init();
        for(int i = 0; i < m; i++)
        {
            scanf("%d %c %d", &ship[i].a, &ship[i].op, &ship[i].b);
            if(ship[i].op == '=')
            {
                if(merge_set(ship[i].a, ship[i].b))
                    sum--;
            }
        }
        for(int i = 0; i < m; i++)
            if(ship[i].op != '=')
            {
                int f = root(ship[i].a), s = root(ship[i].b);
                if(ship[i].op == '>')
                {
                    u[f].push_back(s);
                    in[s]++;
                }
                else
                {
                    u[s].push_back(f);
                    in[f]++;
                }
            }
        top_sort();
    }
    return 0;
}