Codeforces Round #357 (Div. 2) D. Gifts by the List DFS

D. Gifts by the List

链接：

http://codeforces.com/contest/681/problem/D

代码：

 1 #include<iostream>
 2 #include<vector>
 3 using namespace std;
 4 
 5 const int maxn = 1e6 + 7;
 6 int a[maxn], d[maxn], flag;
 7 vector<int> E[maxn];
 8 vector<int> ans;
 9 
10 void dfs(int x, int p)
11 {
12     for (int i = 0; i < E[x].size(); i++)
13     {
14         int u = E[x][i];
15         if (u == p) continue;
16         if (a[u] != a[x] && a[u] != u) flag = 1;
17         dfs(u, x);
18     }
19     if (a[x] == x) ans.push_back(x);
20 }
21 
22 int main()
23 {
24     int n, m;
25     cin >> n >> m;
26     for (int i = 1; i <= m; i++) {
27         int p, q;
28         cin >> p >> q;
29         E[p].push_back(q);
30         E[q].push_back(p);
31         d[q]++;
32     }
33     for (int i = 1; i <= n; i++)
34         cin >> a[i];
35     for (int i = 1; i <= n; i++)
36         if (!d[i])
37             dfs(i, 0);
38     if (flag) {
39         cout << -1 << endl;
40         return 0;
41     }
42     cout << ans.size() << endl;
43     for (int i = 0; i < ans.size(); i++)
44         cout << ans[i] << endl;
45     return 0;
46 }

 

posted @ 2016-09-28 23:33  Flowersea  阅读(155)  评论(0)  编辑  收藏  举报