Poj 2075 tangled in cables

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For N houses, you need to lay cables between the houses so that all houses can be connected. Find the shortest cable. Note that % F is used for double type cables on poj, do not use % lf. Use % lf to show wa.

#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;}