POJ 1751[Highways]

果断Prim不解释。其实Kruskal也可以，刚开始写的时候鉴于内存没敢写。

Const
        maxn=750;
Var
        codes:array[1..maxn,1..2]of longint;
        d:array[1..maxn,1..maxn]of longint;
        lowcost,pre:array[1..maxn]of longint;
        i,j,n:longint;
Procedure prim;
 var
        i,j,k,dist,sum,min,q,x,y:longint;
 begin
        fillchar(d,sizeof(d),0);
        for i:=1 to n-1 do
                for j:=i+1 to n do
                        begin
                                dist:=(codes[i,1]-codes[j,1])*(codes[i,1]-codes[j,1])+(codes[i,2]-codes[j,2])*(codes[i,2]-codes[j,2]);
                                d[i,j]:=dist;
                                d[j,i]:=dist;
                        end;
        readln(q);
        for i:=1 to q do
                begin
                        readln(x,y);
                        d[x,y]:=0;
                        d[y,x]:=0;
                end;
        sum:=0;
        lowcost[1]:=-1;
        for i:=2 to n do
                begin
                        lowcost[i]:=d[1,i];
                        pre[i]:=1;
                end;
        for i:=1 to n-1 do
                begin
                        min:=maxlongint;
                        for k:=1 to n do
                                begin
                                        if (lowcost[k]<>-1)and(lowcost[k]<min) then
                                                begin
                                                        j:=k;
                                                        min:=lowcost[k];
                                                end;
                                end;
                        if min<>0 then writeln(pre[j],' ',j);
                        sum:=sum+min;
                        lowcost[j]:=-1;
                        for k:=1 to n do if d[j,k]<lowcost[k] then
                                begin
                                        lowcost[k]:=d[j,k];
                                        pre[k]:=j;
                                end;
                end;
 end;
BEgin

                        readln(n);

                        for i:=1 to n do
                                begin
                                        for j:=1 to 2 do
                                        read(codes[i,j]);
                                        readln;
                                end;
                        prim;

End.