poj2560

最小生成树

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      #include 
    
      <
    
      iostream
    
      >
    
      
#include 
    
      <
    
      cstdio
    
      >
    
      
#include 
    
      <
    
      cstdlib
    
      >
    
      
#include 
    
      <
    
      cstring
    
      >
    
      
#include 
    
      <
    
      cmath
    
      >
    
      

    
      using
    
       
    
      namespace
    
       std;


    
      #define
    
       maxn 105
    
      


    
      struct
    
       Point
{
 
    
      double
    
       x, y;
} point[maxn];


    
      double
    
       cost[maxn][maxn];

    
      int
    
       n;


    
      double
    
       dis(
    
      int
    
       a, 
    
      int
    
       b)
{
 
    
      return
    
       sqrt((point[a].x 
    
      -
    
       point[b].x) 
    
      *
    
       (point[a].x 
    
      -
    
       point[b].x) 
    
      +
    
       (point[a].y
 
    
      -
    
       point[b].y) 
    
      *
    
       (point[a].y 
    
      -
    
       point[b].y));
}


    
      void
    
       makecost()
{
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 
    
      for
    
       (
    
      int
    
       j 
    
      =
    
       
    
      0
    
      ; j 
    
      <
    
       n; j
    
      ++
    
      )
 cost[i][j] 
    
      =
    
       dis(i, j);
}


    
      double
    
       prim()
{
 
    
      double
    
       lowcost[maxn];
 
    
      bool
    
       vis[maxn];

 memset(vis, 
    
      0
    
      , 
    
      sizeof
    
      (vis));
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 lowcost[i] 
    
      =
    
       
    
      -
    
      1
    
      ;
 lowcost[
    
      0
    
      ] 
    
      =
    
       
    
      0
    
      ;
 vis[
    
      0
    
      ] 
    
      =
    
       
    
      true
    
      ;
 
    
      int
    
       pre 
    
      =
    
       
    
      0
    
      ;
 
    
      double
    
       ans 
    
      =
    
       
    
      0
    
      ;
 
    
      while
    
       (
    
      1
    
      )
 {
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 
    
      if
    
       (lowcost[i] 
    
      >
    
       lowcost[pre] 
    
      +
    
       cost[i][pre] 
    
      ||
    
       lowcost[i] 
    
      ==
    
       
    
      -
    
      1
    
      )
 lowcost[i] 
    
      =
    
       lowcost[pre] 
    
      +
    
       cost[i][pre];
 
    
      int
    
       best 
    
      =
    
       
    
      1000000000
    
      ;;
 pre 
    
      =
    
       
    
      -
    
      1
    
      ;
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 
    
      if
    
       (
    
      !
    
      vis[i] 
    
      &&
    
       lowcost[i] 
    
      <
    
       best)
 {
 best 
    
      =
    
       lowcost[i];
 pre 
    
      =
    
       i;
 }
 
    
      if
    
       (pre 
    
      ==
    
       
    
      -
    
      1
    
      )
 
    
      break
    
      ;
 ans 
    
      +=
    
       lowcost[pre];
 vis[pre] 
    
      =
    
       
    
      true
    
      ;
 lowcost[pre] 
    
      =
    
       
    
      0
    
      ;
 }
 
    
      return
    
       ans;
}


    
      int
    
       main()
{
 
    
      //
    
      freopen("t.txt", "r", stdin);
    
      

    
       scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      n);
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 scanf(
    
      "
    
      %lf%lf
    
      "
    
      , 
    
      &
    
      point[i].x, 
    
      &
    
      point[i].y);
 makecost();
 printf(
    
      "
    
      %.2f\n
    
      "
    
      , prim());
 
    
      return
    
       
    
      0
    
      ;
}