TOJ 2119 Tangled in Cables

描述

You are the owner of SmallCableCo and have purchased the franchise rights for a small town. Unfortunately, you lack enough funds to start your business properly and are relying on parts you have found in an old warehouse you bought. Among your finds is a single spool of cable and a lot of connectors. You want to figure out whether you have enough cable to connect every house in town. You have a map of town with the distances for all the paths you may use to run your cable between the houses. You want to calculate the shortest length of cable you must have to connect all of the houses together.

输入

Only one town will be given in an input.

　　The first line gives the length of cable on the spool as a real number.

　　The second line contains the number of houses, N

　 The next N lines give the name of each house's owner. Each name consists of up to 20 characters {a~z, A~Z,0~9} and contains no whitespace or punctuation.

　　Next line: M, number of paths between houses

　　next M lines in the form

< house name A > < house name B > < distance >

Where the two house names match two different names in the list above
and the distance is a positive real number. There will not be two paths
between the same pair of houses.

输出

The output will consist of a single line. If there is not enough cable to connect all of the houses in the town, output

Not enough cable

If there is enough cable, then output

Need < X > miles of cable

Print X to the nearest tenth of a mile (0.1).

样例输入

100.0
4
Jones
Smiths
Howards
Wangs
5
Jones Smiths 2.0
Jones Howards 4.2
Jones Wangs 6.7
Howards Wangs 4.0
Smiths Wangs 10.0

样例输出

Need 10.2 miles of cable

题目来源

Mid-Atlantic 2004

#include <stdio.h>
#include <string.h>
#define MAXN 350
#define inf 0x3f3f3f3f

int N,M;
char p[MAXN][25];
double map[MAXN][MAXN];
int visited[MAXN];
double dist[MAXN];

int find(char ch[25]){
for(int i=1; i<=N; i++){
if(strcmp(p[i],ch)==0)return i;
}
return 0;
}
double prim(int begin){
double r=0;
for(int i=1; i<=N; i++){
visited[i]=false;
dist[i]=map[begin][i];
}
visited[begin]=true;
for(int j=1; j<N; j++){
int k=-1;
double min=inf;
for(int i=1; i<=N; i++){
if(!visited[i]&&dist[i]<min){
min=dist[i];
k=i;
}
}
if(min!=inf){
r+=min;
}
visited[k]=true;
for(int i=1; i<=N; i++){
if(!visited[i]&&map[k][i]<dist[i]){
dist[i]=map[k][i];
}
}
}
return r;
}
int main(int argc, char *argv[])
{
double len,w;
char a[25],b[25];
while(scanf("%lf",&len)!=EOF){
scanf("%d",&N);
for(int i=1; i<=N; i++){
scanf("%s",p[i]);
}
for(int i=1; i<=N; i++){
for(int j=1; j<=N; j++){
if(i==j)map[i][j]=0;
else map[i][j]=inf;
}
}
scanf("%d",&M);
while(M--){
scanf("%s %s %lf",a,b,&w);
int u=find(a);
int v=find(b);
map[u][v]=w;
map[v][u]=w;
}
double ans=prim(1);
if(ans<=len){
printf("Need %.1lf miles of cable\n",ans);
}else{
printf("Not enough cable\n");
}
}
return 0;
}