prim算法

{prim算法的时间复杂度为O(n^2)，并且与读入的图的边的条数无关，只与
结点数有关，故prim用于求稠密图}
 program prim_example;
 var
  map:array[0..1000,0..1000]of longint; //记录要读入的邻接矩阵
  dist:array[0..1000]of longint;  //边权
  d:array[0..1000]of 0..1;   //加入的集合
  i,j,n,m,min,ans,k:longint;

 procedure prim;
  begin
   dist[1]:=0;
   for i:=1 to n do
    dist[i]:=map[1,i];
   for i:=1 to n-1 do
    begin
     min:=maxlongint;
     k:=0;
     for j:=1 to n do
      if (dist[j]<min)and(d[j]=0) then  //dist[j]小于最小值并且该节点没在d集合中
       begin
        min:=dist[j];
        k:=j;
       end;
   if k<>0 then //说明上步for循环中if语句执行
    begin
     inc(ans,min);
     d[k]:=1;  //将访问过的结点加入集合d
    end;
   for j:=1 to n do
    if (map[k,j]<dist[j])and(d[j]<>1)then //寻求更短的路径
     dist[j]:=map[k,j];
   end;
  end;

 begin
  assign(input,'input.txt');
  reset(input);
  assign(output,'output.txt');
  rewrite(output);
  readln(n);
  for i:=1 to n do
    for j:=1 to n do
     begin
      read(map[i,j]);
      if (i<>j)and(map[i,j]=0) then
       map[i,j]:=maxlongint;   //初始化
     end;
  d[1]:=1;//从第一号结点开始查询
  prim;
  writeln(ans);
  close(input);
  close(output);
 end.