HDU 4251 The Famous ICPC Team Again

最新推荐文章于 2019-12-25 16:39:31 发布

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最新推荐文章于 2019-12-25 16:39:31 发布

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原文链接：http://www.cnblogs.com/bo-tao/archive/2012/07/19/2600025.html

本文介绍了一个基于划分树的数据处理算法实现。通过递归构建划分树并实现特定区间查询的功能，适用于处理大规模数据集中的区间查询问题。代码示例中详细展示了如何通过划分树对整数数组进行排序和查询中间值。

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这个也是一道对划分树的简单的运用：

View Code

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<queue>
#include<set>
#include<map>
#include<cstring>
#include<vector>
using namespace std;
class Node
{
public:
      int num[100024],val[100024];    
}node[20];
int val[100024];
bool cmp( int a , int b )
{
     return a <= b;
}
void build_tree( int l , int r , int deep )
{
     if( l == r ) return ;
     int mid = ( l + r )>>1;
     int issame = mid - l + 1 ,same = 0;
     for( int i = l ; i <= r ; i ++ )
          if( node[deep].val[i] < val[mid] ) issame --;
    int left = l ,right = mid + 1;
    for( int i = l ; i <= r ; i ++ )
    {
          node[deep].num[i] = node[deep].num[i-1];
          if( node[deep].val[i] > val[mid] )
              node[deep+1].val[right++] = node[deep].val[i];
          else if( node[deep].val[i] < val[mid] )
          {
               node[deep+1].val[left++] = node[deep].val[i];
               node[deep].num[i] ++;
          }
          else
          {
              if( same < issame )
              {
                  same ++;
                  node[deep+1].val[left++] = node[deep].val[i];
                  node[deep].num[i] ++;        
              }    
              else     node[deep+1].val[right++] = node[deep].val[i];
          }            
    }
    build_tree( l , mid , deep + 1 );
    build_tree( mid + 1, r ,deep + 1 ); 
}
int find( int a , int b , int k ,int deep, int l ,int r )
{
    //printf( "l=%d,r=%d,s=%d,t=%d,k=%d,dep=%d\n",l,r,a,b,k,deep);system("pause");
     int mid = ( l + r )>>1;
     if( a == b ) return node[deep].val[a];
     int d = node[deep].num[b] - node[deep].num[a-1];
     int s = node[deep].num[a-1] - node[deep].num[l-1];
     int ss = node[deep].num[b] - node[deep].num[l-1];
     int rx =  a - l  + 1 - s,ry = b - l + 1 - ss;
     if( d >= k )  return find( l + s , l + ss - 1 ,k , deep + 1, l , mid );
     else return find( mid + rx , mid + ry , k - d , deep + 1 , mid + 1 , r );
}
int main(  )
{
    int n,m,Case=1,l,r;
    while( scanf( "%d",&n )==1 )
    {
        for( int i = 1 ; i <= n ; i ++ )
        {
            scanf( "%d",&node[0].val[i] );
            val[i] = node[0].val[i];    
        }    
        sort( val+1, val + n + 1, cmp );
        build_tree( 1 , n  , 0 ); 
//        printf( "sfaf" );
        scanf( "%d",&m );
        printf( "Case %d:\n",Case++ );
        for( int i = 0 ; i < m ; i ++ )
        {
             scanf( "%d %d",&l,&r );
             int k = ( r - l )/2 + 1 ;
             printf( "%d\n",find( l  , r , k, 0 , 1, n  ) );    
        }
    }
    //system( "pause" );
    return 0;
}