pta 编程题13 File Transfer

 1 #include <iostream>
 2 #include <vector>
 3 using namespace std;
 4 
 5 vector<int> computers;
 6 
 7 void _union(int a, int b);
 8 int find(int a);
 9 void components();
10 
11 int main()
12 {
13     int n, c1, c2;
14     char c;
15     cin >> n;
16     computers.resize(n + 1, -1);
17     do{
18         cin >> c;
19         switch (c)
20         {
21         case ‘I‘:
22             cin >> c1 >> c2;
23             _union(c1, c2);
24             break;
25         case ‘C‘:
26             cin >> c1 >> c2;
27             if (find(c1) == find(c2))
28                 cout << "yes" << endl;
29             else
30                 cout << "no" << endl;
31             break;
32         case ‘S‘:
33             components();
34             break;
35         }
36     } while (c != ‘S‘);
37     return 0;
38 }
39 
40 void _union(int a, int b)
41 {
42     int root1 = find(a);
43     int root2 = find(b);
44     if (computers[root1] < computers[root2])
45     {
46         computers[root1] += computers[root2];//顺序不能...
47         computers[root2] = root1;//颠倒！
48     }
49     else {
50         computers[root2] += computers[root1];
51         computers[root1] = root2;
52     }
53 }
54 /*
55 int find(int a)
56 {
57     for (; computers[a] > 0; a = computers[a]);
58     return a;
59 }
60 */
61 int find(int a) //带路径压缩的查找
62 {
63     if (computers[a] < 0) return a;
64     else return computers[a] = find(computers[a]);
65 }
66 
67 void components()
68 {
69     int count = 0;
70     for (int i = 1; i < computers.size(); i++)
71     {
72         if (computers[i] < 0) count++;
73     }    
74     if (count > 1)
75         printf("There are %d components.\n", count);
76     else
77         printf("The network is connected.\n");
78 }