算法问题实战策略 GALLERY

 1 #include <iostream>
 2 #include <vector>
 3 
 4 
 5 using namespace std;
 6 
 7 const int N = 10010;
 8 int V;
 9 vector<int> adj[10010];
10 vector<bool> visited;
11 const int UNWATCHED = 0;
12 const int  WATCHED = 1;
13 const int INSTALLED = 2;
14 
15 int installed;
16 
17 int dfs(int here)
18 {
19     visited[here] = true;
20     int children[3] = { 0,0,0 };
21     for (int i = 0; i < adj[here].size(); i++)
22     {
23         int there = adj[here][i];
24         if (!visited[there])
25             ++children[dfs(there)];
26     }
27 
28     //后代节点存在没有监视的节点 在该节点安装摄像头
29     if (children[UNWATCHED]) {
30         ++installed;
31         return INSTALLED;
32     }
33 
34     if (children[INSTALLED]) {
35         return WATCHED;
36     }
37 
38     return UNWATCHED;
39 }
40 
41 int installCamera()
42 {
43     installed = 0;
44     visited = vector<bool>(V, false);
45     for (int u = 0; u < V; ++u) {
46         if (!visited[u] && dfs(u) == UNWATCHED)
47             ++installed;
48     }
49 
50     return installed;
51 }
52 
53 
54 
55 /*
56 3
57 6 5
58 0 1
59 1 2
60 1 3
61 2 5
62 0 4
63 4 2
64 0 1
65 2 3
66 1000 1
67 0 1
68 =====================
69 3
70 2
71 999
72 */
73 
74 int main()
75 {
76     int sampleCount = 0;
77     cin >> sampleCount;
78     while (sampleCount--) {
79         int n, m; visited.clear();
80         for (int i = 0; i < 10010; i++) adj[i].clear();
81         cin >> V >> m;
82         for (int i = 0; i < m; i++) {
83             int a, b;
84             cin >> a >> b;
85             adj[a].push_back(b); 
86             adj[b].push_back(a);
87         }
88         cout << installCamera() << endl;
89     }
90 
91     return 0;
92 }