poj 2075 Tangled in Cables

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
const float INF=0xffffff;
float edge[510][510],len;
int nn,vis[510];
void prime(int x){
int i,j,k;
float mark[510],mi_n;
float sum_i;
for(i=1;i<=nn;i++){
mark[i]=edge[x][i];
vis[i]=0;
}
vis[x]=1;
sum_i=0.0;
for(i=2;i<=nn;i++){
mi_n=INF;
for(j=1;j<=nn;j++){
if(!vis[j]&&mark[j]<mi_n){
mi_n=mark[j];
k=j;
}
}
vis[k]=1;
sum_i+=mi_n;
if(sum_i>=INF)
break;
for(j=1;j<=nn;j++){
if(!vis[j]&&edge[k][j]<mark[j])
mark[j]=edge[k][j];
}
}
if(sum_i<=len)
printf("Need %.1f miles of cable\n",sum_i);
else printf("Not enough cable\n");
}
int main(){
int i,j,a,m,x,y;
float l;
char str1[510][25],str2[25],str3[25];
while(~scanf("%f",&len)){
scanf("%d",&nn);
for(i=1;i<=nn;i++)
for(j=1;j<=nn;j++)
edge[i][j]=INF;
for(i=1;i<=nn;i++)
scanf("%s",str1[i]);
scanf("%d",&m);
while(m--){
scanf("%s %s %f",str2,str3,&l);
for(j=1;j<=nn;j++){
if(!strcmp(str1[j],str2))
x=j;
if(!strcmp(str1[j],str3))
y=j;
}
edge[x][y]=l;
edge[y][x]=l;
}
prime(1);
}
return 0;
}