《数据结构与算法分析：C语言描述》复习——第九章“图论”——拓扑排序

 1 // A simple illustration for topological sort. Graph represented by adjacency matrix.
 2 #include <iostream>
 3 #include <queue>
 4 #include <vector>
 5 using namespace std;
 6 
 7 void topologicalSort(const vector<vector<bool> > &graph, vector<int> &order)
 8 {
 9     int n;
10     int i, j;
11     vector<int> indegree;
12     queue<int> q;
13     
14     n = (int)graph.size();
15     indegree.resize(n, 0);
16     
17     for (i = 0; i < n; ++i) {
18         for (j = 0; j < n; ++j) {
19             if (graph[i][j]) {
20                 ++indegree[j];
21             }
22         }
23     }
24     
25     for (i = 0; i < n; ++i) {
26         if (indegree[i] == 0) {
27             q.push(i);
28             break;
29         }
30     }
31     
32     while (!q.empty()) {
33         i = q.front();
34         q.pop();
35         order.push_back(i);
36         for (j = 0; j < n; ++j) {
37             if (graph[i][j] && (--indegree[j] == 0)) {
38                 q.push(j);
39             }
40         }
41     }
42     
43     indegree.clear();
44 }
45 
46 int main()
47 {
48     vector<vector<bool> > graph;
49     vector<int> order;
50     int n;
51     int nk;
52     int i, j;
53     int tmp;
54     
55     while (cin >> n && n > 0) {
56         graph.resize(n);
57         for (i = 0; i < n; ++i) {
58             graph[i].resize(n, false);
59         }
60         
61         for (i = 0; i < n; ++i) {
62             cin >> nk;
63             for (j = 0; j < nk; ++j) {
64                 cin >> tmp;
65                 graph[i][tmp] = true;
66             }
67         }
68         
69         topologicalSort(graph, order);
70         
71         if ((int)order.size() == n) {
72             for (i = 0; i < n; ++i) {
73                 cout << order[i] << ‘ ‘;
74             }
75             cout << endl;
76         } else {
77             cout << "The graph has a cycle." << endl;
78         }
79         
80         for (i = 0; i < n; ++i) {
81             graph[i].clear();
82         }
83         graph.clear();
84         order.clear();
85     }
86     
87     return 0;
88 }