POJ 1308 Is It A Tree? (并查集)

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <string>
 4 #include <queue>
 5 #include <vector>
 6 #include <map>
 7 #include <algorithm>
 8 #include <cstring>
 9 #include <cctype>
10 #include <cstdlib>
11 #include <cmath>
12 #include <ctime>
13 using    namespace    std;
14 
15 const    int    SIZE = 100005;
16 int    FATHER[SIZE],RANK[SIZE];
17 vector<int>    S;
18 
19 void    ini(int);
20 int    find_father(int);
21 bool    unite(int,int);
22 bool    same(int,int);
23 int    main(void)
24 {
25     int    a,b,count = 0;
26     bool    flag;
27 
28     while(scanf("%d%d",&a,&b) && (a != -1 && b != -1))
29     {
30         flag = true;
31         if(a == 0 && b == 0)
32         {
33             printf("Case %d %s\n",++ count,flag ? "is a tree." : "is not a tree.");
34             continue;
35         }
36         S.clear();
37         S.push_back(a);
38         S.push_back(b);
39         ini(SIZE - 2);
40         flag = unite(a,b);
41         while(scanf("%d%d",&a,&b) && (a || b))
42         {
43             flag &= unite(a,b);
44             S.push_back(a);
45             S.push_back(b);
46         }
47         for(int i = 1;i < S.size();i ++)
48             flag &= same(S[0],S[i]);
49         printf("Case %d %s\n",++ count,flag ? "is a tree." : "is not a tree.");
50     }
51 
52     return    0;
53 }
54 
55 void    ini(int n)
56 {
57     for(int i = 1;i <= n;i ++)
58     {
59         FATHER[i] = i;
60         RANK[i] = 0;
61     }
62 }
63 
64 int    find_father(int n)
65 {
66     if(n == FATHER[n])
67         return    n;
68     return    FATHER[n] = find_father(FATHER[n]);
69 }
70 
71 bool    unite(int x,int y)
72 {
73     x = find_father(x);
74     y = find_father(y);
75 
76     if(x == y)
77         return    false;
78     if(RANK[x] < RANK[y])
79         FATHER[x] = y;
80     else
81     {
82         FATHER[y] = x;
83         if(RANK[x] == RANK[y])
84             RANK[x] ++;
85     }
86     return    true;
87 }
88 
89 bool    same(int x,int y)
90 {
91     return    find_father(x) == find_father(y);
92 }