USACO 2.4 Cow Tours (cowtour)

//Main Idea
//Use floyd algorithm to calculate shortest path of each pair of pastures
//The compute the smallest possible diameter of the new connected field by enumeration
//The key point is that there are exactly two field need to be connected;

/*
ID: haolink1
PROG: cowtour
LANG: C++
*/

//#include <iostream>
#include <fstream>
#include <math.h>       /* sqrt */
#include<iomanip> //std::setiosflags
#define INF (1e40)

using namespace std;

short num =0;
//dis[i][j] means the shortest distance between i,j;
//dis_max[i] means the max distance of shortest path start from i;
double dis[150][150],dis_max[150];
int px[150],py[150];

double dist(int x1,int y1,int x2,int y2){
return sqrt(double(x1-x2)*(x1-x2) + double(y1-y2)*(y1-y2));
}

void floyd(){
for(short k = 0; k < num; k++){
for(short i = 0; i < num; i++){
for(short j =0; j < num; j++){
if(dis[i][k]+dis[k][j] < dis[i][j])
dis[i][j] = dis[i][k]+dis[k][j];
}
}
}
//Note: reset the dis[i][i] to INF in case
//it will influence the dis_max[i];
for(short i = 0; i < num; i++){
dis[i][i] = INF;
}
}
/*
void PrintDist(){
for(short i = 0; i < num; i++){
for(short j = 0; j < num; j++){
cout<< dis[i][j] <<" ";
}
cout << endl;
}

}
*/

int main(){
ifstream fin("cowtour.in");
fin >> num;
for(short i = 0; i < num; i++){
fin >> px[i];
fin >> py[i];
}
for(short i = 0; i < num; i++){
char val[150];
fin >> val;
for(short j = 0; j < num; j++){
if(val[j] == '1'){
dis[i][j] = dist(px[i],py[i],px[j],py[j]);
}else{
dis[i][j] = INF;
}
}
}
//PrintDist();
floyd();
//PrintDist();
double d_max = 0;
for(short i = 0; i < num; i++){
double tmp_max = 0;
for(short j = 0; j < num; j++){
if(dis[i][j] > tmp_max && dis[i][j] < INF)
tmp_max = dis[i][j];
}
dis_max[i] = tmp_max;
if(tmp_max > d_max)
d_max = tmp_max;
}
double d_min = INF;
for(short i = 0; i < num-1; i++){
for(short j = i+1; j < num; j++){
if(i != j && dis[i][j] == INF){
double temp = dist(px[i],py[i],px[j],py[j]);
if(temp+dis_max[i]+dis_max[j] < d_min)
d_min = temp+dis_max[i]+dis_max[j];
}
}
}
ofstream fout("cowtour.out");
//fout <<setiosflags(ios::fixed)<<setiosflags(ios::right)<<setprecision(6)<<(d_max > d_min ? d_max:d_min) << endl;
fout <<setiosflags(ios::fixed)<<setprecision(6)<<(d_max > d_min ? d_max:d_min) << endl;
return 0;
}