poj2299

树状数组

View Code

   
     

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

    
      using
    
       
    
      namespace
    
       std;


    
      #define
    
       maxn 500005
    
      


    
      struct
    
       Elem
{
 
    
      int
    
       p, v;
}s[maxn];


    
      int
    
       f[maxn];

    
      int
    
       pos[maxn];

    
      int
    
       ar[maxn];


    
      bool
    
       
    
      operator
    
       
    
      <
    
       (
    
      const
    
       Elem 
    
      &
    
      a, 
    
      const
    
       Elem 
    
      &
    
      b)
{
 
    
      return
    
       a.v 
    
      <
    
       b.v;
}


    
      int
    
       lowb(
    
      int
    
       t)
{
 
    
      return
    
       t 
    
      &
    
       (
    
      -
    
      t);
}


    
      void
    
       add(
    
      int
    
       i, 
    
      int
    
       v)
{
 
    
      for
    
       (; i 
    
      <
    
       maxn; ar[i] 
    
      +=
    
      v, i 
    
      +=
    
       lowb(i));
}


    
      int
    
       sum(
    
      int
    
       i)
{
 
    
      int
    
       s 
    
      =
    
       
    
      0
    
      ;
 
    
      for
    
       (; i 
    
      >
    
       
    
      0
    
      ; s 
    
      +=
    
       ar[i], i 
    
      -=
    
       lowb(i));
 
    
      return
    
       s;
}


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

    
       
    
      int
    
       n;
 memset(ar, 
    
      0
    
      , 
    
      sizeof
    
      (ar));
 
    
      while
    
       (scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      n), n)
 {
 memset(ar, 
    
      0
    
      , 
    
      sizeof
    
      (ar));
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 {
 scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      f[i]);
 s[i].v 
    
      =
    
       f[i];
 s[i].p 
    
      =
    
       i;
 }
 sort(s, s 
    
      +
    
       n);
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      0
    
      ; i 
    
      <
    
       n; i
    
      ++
    
      )
 pos[s[i].p] 
    
      =
    
       i 
    
      +
    
       
    
      1
    
      ;
 
    
      long
    
       
    
      long
    
       ans 
    
      =
    
       
    
      0
    
      ;
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       n 
    
      -
    
       
    
      1
    
      ; i 
    
      >=
    
       
    
      0
    
      ; i
    
      --
    
      )
 {
 ans 
    
      +=
    
       sum(pos[i] 
    
      -
    
       
    
      1
    
      );
 add(pos[i], 
    
      1
    
      );
 }
 printf(
    
      "
    
      %lld\n
    
      "
    
      , ans);
 }
 
    
      return
    
       
    
      0
    
      ;
}