HDU 1301  Jungle Roads

Jungle Roads

Time Limit: 2000/1000 MS
(Java/Others)    Memory Limit:
65536/32768 K (Java/Others)
Total Submission(s): 1735
   Accepted Submission(s):
1259

Problem Description



The Head Elder of the tropical island of Lagrishan has a
problem. A burst of foreign aid money was spent on extra roads
between villages some years ago. But the jungle overtakes roads
relentlessly, so the large road network is too expensive to
maintain. The Council of Elders must choose to stop maintaining
some roads. The map above on the left shows all the roads in use
now and the cost in aacms per month to maintain them. Of course
there needs to be some way to get between all the villages on
maintained roads, even if the route is not as short as before. The
Chief Elder would like to tell the Council of Elders what would be
the smallest amount they could spend in aacms per month to maintain
roads that would connect all the villages. The villages are labeled
A through I in the maps above. The map on the right shows the roads
that could be maintained most cheaply, for 216 aacms per month.
Your task is to write a program that will solve such
problems. 

The input consists of one to 100 data sets, followed by a
final line containing only 0. Each data set starts with a line
containing only a number n, which is the number of villages, 1
< n < 27, and the villages are
labeled with the first n letters of the alphabet, capitalized. Each
data set is completed with n-1 lines that start with village labels
in alphabetical order. There is no line for the last village. Each
line for a village starts with the village label followed by a
number, k, of roads from this village to villages with labels later
in the alphabet. If k is greater than 0, the line continues with
data for each of the k roads. The data for each road is the village
label for the other end of the road followed by the monthly
maintenance cost in aacms for the road. Maintenance costs will be
positive integers less than 100. All data fields in the row are
separated by single blanks. The road network will always allow
travel between all the villages. The network will never have more
than 75 roads. No village will have more than 15 roads going to
other villages (before or after in the alphabet). In the sample
input below, the first data set goes with the map
above. 

The output is one integer per line for each data set: the
minimum cost in aacms per month to maintain a road system that
connect all the villages. Caution: A brute force solution that
examines every possible set of roads will not finish within the one
minute time limit. 
 

Sample Input
9
A 2 B 12 I 25
B 3 C 10 H 40 I 8
C 2 D 18 G 55
D 1 E 44
E 2 F 60 G 38
F 0
G 1 H 35
H 1 I 35
3
A 2 B 10 C 40
B 1 C 20
0
 

Sample Output
216
30
 

Source
Mid-Central USA 2002
 

Recommend
Eddy
最小生成树，1A
代码：

#include<stdio.h>
#include<stdlib.h>
struct point{
int begin,end;
int len;
}map[900];
int flag[30];
int cmp(const void *a,const void *b)
{
struct point *c,*d;
c=(struct point *)a;
d=(struct point *)b;
return c->len-d->len;
}
int father(int x)
{
if(flag[x]==x)
return x;
flag[x]=father(flag[x]);
return flag[x];
}
int main()
{
int N,i,j,k,b,sum,fa,fb,num;
char s,a;
while(scanf("%d",&N),N)
{
k=0;
getchar();
for(i=1;i<=N-1;i++)
{
scanf("%c %d",&s,&num);
for(j=1;j<=num;j++)
{
scanf(" %c %d",&a,&b);
map[k].begin=s-'A';
map[k].end=a-'A';
map[k++].len=b;
}
getchar();
}
for(i=0;i<=N;i++)
flag[i]=i;
qsort(map,k,sizeof(map[0]),cmp);
sum=0;
for(i=0;i<k;i++)
{
fa=father(map[i].begin);
fb=father(map[i].end);
if(fa!=fb){
sum+=map[i].len;
if(fa>fb)
flag[fa]=fb;
else flag[fb]=fa;
}
}
printf("%d\n",sum);
}
return 0;
}