畅通工程再续（MST）

#include<stdio.h>
#include<algorithm>
#include<math.h>
#define Max 0x3f3f3f3f
using namespace std;
struct island
{
    double x , y ;
}land[110];

int n , fa[110] ;
int in ;

struct edge
{
    int u , v ;
    double w ;
}e[105*52+2];

void binary (island a , int key , int l , int r )
{
    if ( l >= r) {
        return ;
    }
    int mid = (l + r) / 2 ;
    binary (a , key , l , mid ) ;
    binary (a , key , mid + 1 , r ) ;
    double dis = (a.x - land[mid].x) * (a.x - land[mid].x) + (a.y - land[mid].y) * (a.y - land[mid].y) ;

    if ( dis <= 1000 * 1000 && dis >= 10 * 10 ) {
        e[in].u =  key ;
        e[in].v = mid ;
        e[in].w = sqrt (dis) ;
        in++ ;
    }
}

bool cmp (edge a , edge b)
{
    return a.w < b.w ;
}

int find (int x)
{
    return fa[x] == x ? x : find (fa[x]) ;
}

void kruskal ()
{
    sort ( e + 1 , e + in , cmp ) ;
    int x , y ;
    double ans = 0;
    for (int i = 1 ; i < in ; i++) {
        x = find (e[i].u) ;
        y = find (e[i].v) ;
        if ( x != y) {
            ans += e[i].w ;
            fa[x] = y ;
        }
    }
    printf ("%.1f\n" , 100.0 * ans ) ;
}
int main ()
{
   // freopen ("a.txt" , "r" , stdin ) ;
    int T;
    scanf ("%d" , &T ) ;
    int x , y ;
    int cnt ;
    while (T--) {
            in = 1 ;//RE ‘s reason
            cnt = 0 ;
        scanf ("%d" , &n ) ;
        for (int i = 1 ; i <= n ; i++)
            fa[i] = i ;
        for (int i = 1 ; i <= n ; i++) {
            scanf ("%lf%lf" , &land[i].x , &land[i].y ) ;
        }
        for (int i = 1 ; i < n ; i++ ) {//建立 u , v , w
            binary ( land[i] , i , i + 1 , n + 1) ;
        }
       //To determine whether the connectivity
        for (int i = 1 ; i < in ; i++) {
            x = find (e[i].u) ;
            y = find (e[i].v) ;
            fa[x] = y;
        }
        for (int i = 1 ; i <= n ; i++) {
            if (fa[i] == i )
                cnt++ ;
            if (cnt > 1)
                break ;
        }

        for (int i = 1 ; i <= n ; i++)
            fa[i] = i ;

        if ( cnt > 1)
            puts ("oh!") ;
        else
            kruskal () ;
    }
    return 0 ;
}