poj 2560 Freckles

Freckles

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 8483		Accepted: 4028

Description

In an episode of the Dick Van Dyke show, little Richie connects the freckles on his Dad's back to form a picture of the Liberty Bell. Alas, one of the freckles turns out to be a scar, so his Ripley's engagement falls through. 

Consider Dick's back to be a plane with freckles at various (x,y) locations. Your job is to tell Richie how to connect the dots so as to minimize the amount of ink used. Richie connects the dots by drawing straight lines between pairs, possibly lifting the
pen between lines. When Richie is done there must be a sequence of connected lines from any freckle to any other freckle.
Input

The first line contains 0 < n <= 100, the number of freckles on Dick's back. For each freckle, a line follows; each following line contains two real numbers indicating the (x,y) coordinates of the freckle.
Output

Your program prints a single real number to two decimal places: the minimum total length of ink lines that can connect all the freckles.
Sample Input

3
1.0 1.0
2.0 2.0
2.0 4.0

Sample Output
3.41

分析：最小生成树，用并查集优化的KURUSKAL做。

代码
const

  maxn=5000;

var

  a,b,q:array[0..maxn] of real;

  p:array[0..maxn] of longint;

  c:array[0..maxn,1..2] of longint;

  i,j,n,m:longint;

  ans:real;

procedure qsort(l,r:longint);

var

  i,j:longint;

  k:real;

begin

  if l>=r then exit;

  i:=l;j:=r;

  k:=q[(l+r) div 2];

  repeat

    while q[i]<k do inc(i);

    while q[j]>k do dec(j);

    if i<=j then

      begin

        c[0]:=c[i];c[i]:=c[j];c[j]:=c[0];

        q[0]:=q[i];q[i]:=q[j];q[j]:=q[0];

        inc(i);dec(j);

      end;

  until i>j;

  qsort(l,j);qsort(i,r);

end;

function find(x:longint):longint;

begin

  if p[x]=x then exit(x);

  p[x]:=find(p[x]);

  exit(p[x]);

end;

procedure main;

var

  i,j,p1,p2:longint;

begin

  for i:=1 to m do

    begin

      p1:=find(c[i,1]);

      p2:=find(c[i,2]);

      if p1<>p2 then

        begin

         p[p2]:=p1;

         ans:=ans+q[i];

        end;

    end;

end;

begin

  readln(n);

  for i:=1 to n do

    begin

      readln(a[i],b[i]);

      p[i]:=i;

    end;

  for i:=1 to n do

    for j:=i+1 to n do

      begin

        inc(m);

        c[m,1]:=i;

        c[m,2]:=j;

        q[m]:=sqrt(sqr(a[i]-a[j])+sqr(b[i]-b[j]));

      end;

  qsort(1,m);

  main;

  writeln(ans:0:2);

end.