poj2367 Genealogical tree

思路：

拓扑排序，这里是用染色的dfs实现的。在有环的情况下可以判断出来，没有环的情况下输出拓扑排序序列。

实现：

#include <vector>
#include <cstring>
#include <iostream>
#include <algorithm>
#define w 0
#define g 1
#define b 2
using namespace std;
const int N = 105;
int G[N][N];
vector<int> res, vis;
bool cycle;
int n, m;
void init()
{
    cycle = false;
    cin >> n;
    memset(G, 0, sizeof G);
    for (int i = 0; i <= n; i++) vis.push_back(w);
    int x;
    for (int i = 1; i <= n; i++)
    {
        while (cin >> x, x)
        {
            G[i][x] = 1;
        }
    }
}
void dfs(int u)
{
    if (vis[u] == b) return;
    if (vis[u] == g) { cycle = true; return; }
    vis[u] = g;
    for (int i = n; i >= 1; i--)
    {
        if (G[u][i]) dfs(i);
    }
    vis[u] = b;
    res.push_back(u);
    return;
}
void topsort()
{
    for (int i = n; i >= 1; i--)
    {
        if (vis[i] == w) dfs(i);
    }
    reverse(res.begin(), res.end());
}
int main()
{
    init();
    topsort();
    if (cycle) cout << "There is a cycle in G!" << endl;
    else
    {
        for (int i = 0; i < res.size(); i++)
            cout << res[i] << " ";
        cout << endl;
    }
    return 0;
}