POJ2031 & ZOJ1718[Building a Space Station]

MST，不过这个题用Prim可能会快点，表示我写的Kruskal。

两点之间的距离如果比两点半径和小那么建图时把两点距离置为0，这样就保证了重叠和相交的情况。

Var
        a,b,f:array[1..11000]of longint;
        e,x,y,z,r:array[1..10000]of extended;
        n,ans,m:longint;
        sum:extended;
Function cf(x:extended):extended;
 begin
        exit(x*x);
 end;
Procedure addgraph(x,y:longint;z:extended);
 begin
        inc(m);
        a[m]:=x;
        b[m]:=y;
        e[m]:=z;

 end;
Procedure init;
 var
        i,j:longint;
        dis:extended;
 begin
        readln(n);
        if n=0 then halt;
        m:=0;
        for i:=1 to n do readln(x[i],y[i],z[i],r[i]);
        fillchar(f,sizeof(f),0);
        for i:=1 to n do
                for j:=1 to n do
                        if i<>j then
                                begin
                                        dis:=sqrt(cf(x[i]-x[j])+cf(y[i]-y[j])+cf(z[i]-z[j]));
                                        if dis<=r[i]+r[j] then dis:=0 else dis:=dis-r[i]-r[j];
                                        addgraph(i,j,dis);
                                end;
 end;
Procedure qsort(l,r:longint);
 var
 i,j,y:longint;
 x,z:extended;
 begin
        i:=l;j:=r;x:=e[(l+r)shr 1];
        Repeat
                while e[i]<x do inc(i);
                while e[j]>x do dec(j);
                if i<=j then
                        begin
                                y:=a[i];a[i]:=a[j];a[j]:=y;
                                y:=b[i];b[i]:=b[j];b[j]:=y;
                                z:=e[i];e[i]:=e[j];e[j]:=z;
                                inc(i);dec(j);
                        end;
        Until i>j;
        if i<r then qsort(i,r);
        if l<j then qsort(l,j);
 end;
Function find(x:longint):longint;
 var
        k:longint;
 begin
        k:=x;
        while f[k]<>0 do k:=f[k];
        find:=k;
 end;
Procedure kruskal;
 var
        i,j,p,q:longint;
 begin
        qsort(1,m);
        sum:=0;
        ans:=0; 
        for i:=1 to m do
                begin
                        p:=find(a[i]);
                        q:=find(b[i]);
                        if p<>q then
                                begin
                                        f[q]:=p;
                                        sum:=sum+e[i];
                                        inc(ans);

                                end;
                if ans>=n-1 then break;
                end;
        writeln(sum:0:3);
 end;
Begin
     n:=1;
     while n<>0 do
        begin
                init;
                kruskal;
        end;
End.