题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2181
哈密顿绕行世界问题
Time Limit: 3000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 2362 Accepted Submission(s): 1490
Problem Description
一个规则的实心十二面体，它的 20个顶点标出世界著名的20个城市，你从一个城市出发经过每个城市刚好一次后回到出发的城市。
Input
前20行的第i行有3个数,表示与第i个城市相邻的3个城市.第20行以后每行有1个数m,m<=20,m>=1.m=0退出.
Output
输出从第m个城市出发经过每个城市1次又回到m的所有路线,如有多条路线,按字典序输出,每行1条路线.每行首先输出是第几条路线.然后个一个: 后列出经过的城市.参看Sample output
Sample Input
2 5 20
1 3 12
2 4 10
3 5 8
1 4 6
5 7 19
6 8 17
4 7 9
8 10 16
3 9 11
10 12 15
2 11 13
12 14 20
13 15 18
11 14 16
9 15 17
7 16 18
14 17 19
6 18 20
1 13 19
5
0
Sample Output
1: 5 1 2 3 4 8 7 17 18 14 15 16 9 10 11 12 13 20 19 6 5
2: 5 1 2 3 4 8 9 10 11 12 13 20 19 18 14 15 16 17 7 6 5
3: 5 1 2 3 10 9 16 17 18 14 15 11 12 13 20 19 6 7 8 4 5
4: 5 1 2 3 10 11 12 13 20 19 6 7 17 18 14 15 16 9 8 4 5
5: 5 1 2 12 11 10 3 4 8 9 16 15 14 13 20 19 18 17 7 6 5
6: 5 1 2 12 11 15 14 13 20 19 18 17 16 9 10 3 4 8 7 6 5
7: 5 1 2 12 11 15 16 9 10 3 4 8 7 17 18 14 13 20 19 6 5
8: 5 1 2 12 11 15 16 17 18 14 13 20 19 6 7 8 9 10 3 4 5
9: 5 1 2 12 13 20 19 6 7 8 9 16 17 18 14 15 11 10 3 4 5
10: 5 1 2 12 13 20 19 18 14 15 11 10 3 4 8 9 16 17 7 6 5
11: 5 1 20 13 12 2 3 4 8 7 17 16 9 10 11 15 14 18 19 6 5
12: 5 1 20 13 12 2 3 10 11 15 14 18 19 6 7 17 16 9 8 4 5
13: 5 1 20 13 14 15 11 12 2 3 10 9 16 17 18 19 6 7 8 4 5
14: 5 1 20 13 14 15 16 9 10 11 12 2 3 4 8 7 17 18 19 6 5
15: 5 1 20 13 14 15 16 17 18 19 6 7 8 9 10 11 12 2 3 4 5
16: 5 1 20 13 14 18 19 6 7 17 16 15 11 12 2 3 10 9 8 4 5
17: 5 1 20 19 6 7 8 9 10 11 15 16 17 18 14 13 12 2 3 4 5
18: 5 1 20 19 6 7 17 18 14 13 12 2 3 10 11 15 16 9 8 4 5
19: 5 1 20 19 18 14 13 12 2 3 4 8 9 10 11 15 16 17 7 6 5
20: 5 1 20 19 18 17 16 9 10 11 15 14 13 12 2 3 4 8 7 6 5
21: 5 4 3 2 1 20 13 12 11 10 9 8 7 17 16 15 14 18 19 6 5
22: 5 4 3 2 1 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5
23: 5 4 3 2 12 11 10 9 8 7 6 19 18 17 16 15 14 13 20 1 5
24: 5 4 3 2 12 13 14 18 17 16 15 11 10 9 8 7 6 19 20 1 5
25: 5 4 3 10 9 8 7 6 19 20 13 14 18 17 16 15 11 12 2 1 5
26: 5 4 3 10 9 8 7 17 16 15 11 12 2 1 20 13 14 18 19 6 5
27: 5 4 3 10 11 12 2 1 20 13 14 15 16 9 8 7 17 18 19 6 5
28: 5 4 3 10 11 15 14 13 12 2 1 20 19 18 17 16 9 8 7 6 5
29: 5 4 3 10 11 15 14 18 17 16 9 8 7 6 19 20 13 12 2 1 5
30: 5 4 3 10 11 15 16 9 8 7 17 18 14 13 12 2 1 20 19 6 5
31: 5 4 8 7 6 19 18 17 16 9 10 3 2 12 11 15 14 13 20 1 5
32: 5 4 8 7 6 19 20 13 12 11 15 14 18 17 16 9 10 3 2 1 5
33: 5 4 8 7 17 16 9 10 3 2 1 20 13 12 11 15 14 18 19 6 5
34: 5 4 8 7 17 18 14 13 12 11 15 16 9 10 3 2 1 20 19 6 5
35: 5 4 8 9 10 3 2 1 20 19 18 14 13 12 11 15 16 17 7 6 5
36: 5 4 8 9 10 3 2 12 11 15 16 17 7 6 19 18 14 13 20 1 5
37: 5 4 8 9 16 15 11 10 3 2 12 13 14 18 17 7 6 19 20 1 5
38: 5 4 8 9 16 15 14 13 12 11 10 3 2 1 20 19 18 17 7 6 5
39: 5 4 8 9 16 15 14 18 17 7 6 19 20 13 12 11 10 3 2 1 5
40: 5 4 8 9 16 17 7 6 19 18 14 15 11 10 3 2 12 13 20 1 5
41: 5 6 7 8 4 3 2 12 13 14 15 11 10 9 16 17 18 19 20 1 5
42: 5 6 7 8 4 3 10 9 16 17 18 19 20 13 14 15 11 12 2 1 5
43: 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 2 3 4 5
44: 5 6 7 8 9 16 17 18 19 20 1 2 12 13 14 15 11 10 3 4 5
45: 5 6 7 17 16 9 8 4 3 10 11 15 14 18 19 20 13 12 2 1 5
46: 5 6 7 17 16 15 11 10 9 8 4 3 2 12 13 14 18 19 20 1 5
47: 5 6 7 17 16 15 11 12 13 14 18 19 20 1 2 3 10 9 8 4 5
48: 5 6 7 17 16 15 14 18 19 20 13 12 11 10 9 8 4 3 2 1 5
49: 5 6 7 17 18 19 20 1 2 3 10 11 12 13 14 15 16 9 8 4 5
50: 5 6 7 17 18 19 20 13 14 15 16 9 8 4 3 10 11 12 2 1 5
51: 5 6 19 18 14 13 20 1 2 12 11 15 16 17 7 8 9 10 3 4 5
52: 5 6 19 18 14 15 11 10 9 16 17 7 8 4 3 2 12 13 20 1 5
53: 5 6 19 18 14 15 11 12 13 20 1 2 3 10 9 16 17 7 8 4 5
54: 5 6 19 18 14 15 16 17 7 8 9 10 11 12 13 20 1 2 3 4 5
55: 5 6 19 18 17 7 8 4 3 2 12 11 10 9 16 15 14 13 20 1 5
56: 5 6 19 18 17 7 8 9 16 15 14 13 20 1 2 12 11 10 3 4 5
57: 5 6 19 20 1 2 3 10 9 16 15 11 12 13 14 18 17 7 8 4 5
58: 5 6 19 20 1 2 12 13 14 18 17 7 8 9 16 15 11 10 3 4 5
59: 5 6 19 20 13 12 11 10 9 16 15 14 18 17 7 8 4 3 2 1 5
60: 5 6 19 20 13 14 18 17 7 8 4 3 10 9 16 15 11 12 2 1 5
题解：dfs记录路径的时候要巧妙的利用题意，这个题中给了固定的点的个数，那么统计的时候直接for(int i = 0; i < 20; i++)即可
记录20个点的父亲就可以，如果不知道路径上到底有多上个点，那么就通过其他的特性来判断结束从父节点倒退的终止条件
再说字典序，用矩阵存储边就成了自动利用字典序的最好的方法
1 #include<cstdio> 2 #include<cstring> 3 #include<string> 4 #include<iostream> 5 #include<algorithm> 6 using namespace std; 7 #define N 25 8 int mp[N][N]; 9 bool vis[N]; 10 int fa[N]; 11 int ans[N]; 12 void dfs(int tm, int s, int sum, int &cnt) 13 { 14 if( sum==20 ){ 15 if(!mp[s][tm]) return; 16 printf("%d: ",cnt); 17 int f = s; 18 //int c = 1; 19 for(int i = 1; i< 20; i++){ 20 ans[i] = fa[f]; 21 f = fa[f]; 22 } 23 for(int i = 19; i > 0; i--){ 24 printf("%d ",ans[i]); 25 } 26 printf("%d %d ",s,tm); 27 cnt = cnt+1; 28 return; 29 } 30 for(int i = 1; i <= 20; i++){ 31 if(!vis[i]&&mp[s][i]){ 32 // puts("haha"); 33 vis[i] = 1; 34 fa[i] = s; 35 dfs(tm,i,sum+1,cnt); 36 vis[i] = 0; 37 } 38 } 39 return; 40 } 41 int main() 42 { 43 memset(mp,0,sizeof(mp)); 44 for(int i = 1; i <= 20; i++) 45 { 46 int x, y, z; 47 scanf("%d%d%d",&x,&y,&z); 48 mp[i][x] = mp[x][i] = 1; 49 mp[i][y] = mp[y][i] = 1; 50 mp[i][z] = mp[z][i] = 1; 51 } 52 int s; 53 while(~scanf("%d",&s)) 54 { 55 if(s==0) return 0; 56 memset(vis,0,sizeof(vis)); 57 memset(fa,0,sizeof(fa)); 58 memset(ans,0,sizeof(ans)); 59 int cnt = 1; 60 vis[s] = 1; 61 fa[s] = s; 62 dfs(s,s,1,cnt); 63 } 64 return 0; 65 }