并查集。需要考虑入度。
1 #include <stdio.h>
2 #include <string.h>
3
4 #define MAXNUM 10005
5
6 int bin[MAXNUM];
7 int degree[MAXNUM];
8 int nums[MAXNUM];
9
10 int find(int x) {
11 int r = x;
12
13 while (bin[r] != r)
14 r = bin[r];
15
16 return r;
17 }
18
19 int main() {
20 int x, y, fx, fy, n, case_n = 0;
21 int i, flg;
22
23 while (1) {
24 scanf("%d %d", &x, &y);
25 if (x<0 && y<0)
26 break;
27 memset(degree, 0, sizeof(degree));
28 n = 0;
29 ++case_n;
30 if (x==0 && y==0) {
31 printf("Case %d is a tree.\n", case_n);
32 continue;
33 }
34 for (i=0; i<MAXNUM; ++i)
35 bin[i] = i;
36 fx = find(x);
37 fy = find(y);
38 bin[fy] = fx;
39 degree[y]++;
40 flg = 1;
41 nums[n++] = x;
42 nums[n++] = y;
43 while (1) {
44 scanf("%d %d", &x, &y);
45 if (x==0 && y==0)
46 break;
47 fx = find(x);
48 fy = find(y);
49 if (fx != fy) {
50 bin[fy] = fx;
51 degree[y]++;
52 } else {
53 bin[fy] = fx;
54 degree[y]++;
55 flg = 0;
56 }
57 nums[n++] = x;
58 nums[n++] = y;
59 }
60 fx = find(nums[0]);
61 for (i=1; i<n; ++i) {
62 fy = find(nums[i]);
63 if (fx != fy) {
64 flg = 0;
65 break;
66 }
67 }
68 for (i=0; i<n; ++i) {
69 if (degree[nums[i]] > 1) {
70 flg = 0;
71 break;
72 }
73 }
74 if (flg)
75 printf("Case %d is a tree.\n", case_n);
76 else
77 printf("Case %d is not a tree.\n", case_n);
78 }
79
80 return 0;
81 }
【HDOJ】1325 Is It A Tree?,布布扣,bubuko.com
时间： 2024-10-25 04:09:25