P1265-公路修建

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 #define pb push_BACk
 4 #define _for(i,a,b) for(int i = (a);i < (b);i ++)
 5 #define INF 100000003
 6 #define ll long long
 7 inline ll read()
 8 {
 9     ll ans = @H_675_42@0;
10     char ch = getchar(),last = ‘ ‘;
11     while(!isdigit(ch)) last = ch,ch = getchar();
12     while(isdigit(ch)) ans = (ans << @H_675_42@1) + (ans << @H_675_42@3) + ch - ‘0‘,ch = getchar();
13     if(last == ‘-‘) ans = -ans;
14     return ans;
15 }
16 inline void write(ll X)
17 {
18     if(x < @H_675_42@0) x = -x,putchar(‘-‘);
19     if(x >= @H_675_42@10) write(x / @H_675_42@10);
20     putchar(x % @H_675_42@10 + ‘0‘);
21 }
22 
23 double mincost[@H_675_42@5003];
24 bool used[@H_675_42@5003];
25 
26 int V;
27 struct P
28 {
29     int x;
30     int y;
31 };
32 P a[@H_675_42@5003];
33 double cal(P a,P b)
34 {
35     return sqrt((double)(a.x-b.X)*(a.x-b.X)+(double)(a.y-b.y)*(a.y-b.y));
36 }
37 double MST()
38 {
39     _for(i,@H_675_42@1,V+@H_675_42@1)
40     {
41         mincost[i] = INF;
42         used[i] = false;
43     }
44 
45     mincost[@H_675_42@1] = @H_675_42@0;
46     double res = @H_675_42@0;
47 
48     while(@H_675_42@1)
49     {
50         int v = -@H_675_42@1;
51         _for(u,V+@H_675_42@1)
52         if(!used[u] && (v==-@H_675_42@1 || mincost[u] < mincost[v]))
53             v = u;
54 
55         if(v==-@H_675_42@1) break;
56         used[v] = true;
57         res += mincost[v];
58 
59         _for(u,V+@H_675_42@1)
60             mincost[u] = min(mincost[u],cal(a[v],a[u]));
61     }
62     return res;
63 }
64 
65 int main()
66 {
67     V = read();
68     _for(i,V+@H_675_42@1)
69         a[i].x = read(),a[i].y = read();
70     
71     printf("%.2lf\n",MST());
72     return @H_675_42@0;
73 }