POJ 2349[Arctic Network]

这个题Prim是比较快的，用Kruskal要700+ms，幸亏时限是2000ms……

这个题就是建图之后求最小生成树中第p-s小的那条边，用kruskal比较容易理解~

Var
        a,b,f,x,y:array[1..1000000]of longint;
        e:array[1..1000000]of extended;
        n,m,ans,p,s,fu,i:longint;
        sum:extended;
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;
 begin
        readln(s,p);
        m:=0;
        fillchar(f,sizeof(f),0);
        for i:=1 to p do readln(x[i],y[i]);
        for i:=1 to p do
                for j:=1 to p do if i<>j then
                        begin
                                addgraph(i,j,sqrt((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j])));
                        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,pp,qq:longint;
 begin
        qsort(1,m);
        sum:=0;
        ans:=0;
        for i:=1 to m do
                begin
                        pp:=find(a[i]);
                        qq:=find(b[i]);
                        if pp<>qq then
                                begin
                                        f[qq]:=pp;

                                        sum:=sum+e[i];
                                        inc(ans);
                                end;
                if ans=p-s then break;
                end;
        writeln(e[i]:0:2);
 end;
Begin
        readln(fu);
        for i:=1 to fu do
        begin
        init;
        kruskal;
        end;

End.