《数据结构与算法分析：C语言描述》复习——第九章“图论”——无权值的最短路径问题

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