HDU 1698 Just a Hook

该题是一道简单的线段树题目，关键就是区间更新的问题，更新时不要更新到每个节点，而是更新到他们的包括他们的所有节点的父节点就可以了，当有新的更新时，就把父节点的原先的更新更新到子节点，这样就可以尽量保证不必要的重复更新。

#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
class Node
{
public:
    int l,r,mid;
    int value;
};
Node tree[400024];
class Tree
{
public:
     void Maketree( int l,int r,int cnt );
     void Change( int l,int r,int num,int cnt );
     int Sum( int l,int r ,int cnt);    
};
void Tree::Maketree(int l,int r,int cnt )
{
   if( l == r )
   {
      tree[cnt].r= tree[cnt].l=tree[cnt].mid = l;
      tree[cnt].value = 1;
      return ;
    }    
   else
   {
      tree[cnt].l=l;
      tree[cnt].r=r;
      tree[cnt].mid = ( l+r )>>1;
      tree[cnt].value = 1;
      Maketree( l , tree[cnt].mid , cnt*2 );
      Maketree( tree[cnt].mid + 1, r ,cnt*2+1 );        
   }
}
void Tree::Change(int l,int r,int num,int cnt)
{
   if( l<=tree[cnt].l&&r>=tree[cnt].r )
   {
       tree[cnt].value = num;
       return;        
   }
   else
   {
      if( tree[cnt].value == num )  return;
      else
      {
         if( tree[cnt].value>0 )
         {
             tree[cnt*2].value  = tree[cnt*2+1].value = tree[cnt].value;
             tree[cnt].value = 0;        
         }
        if( l>tree[cnt].mid ) Change( l , r ,num,cnt*2+1 );
        else
        {
           if( r<=tree[cnt].mid ) Change( l ,r ,num ,cnt*2 );
           else
           {
               Change( l  ,tree[cnt].mid,num,cnt*2 );
               Change( tree[cnt].mid +1 , r ,num , cnt*2+1 );        
           }    
        }        
      }        
   }    
}
int Tree::Sum( int l,int r,int cnt )
{
   if( tree[cnt].value > 0 )
     return tree[cnt].value*( tree[cnt].r - tree[cnt].l +1 );
    else if( l> tree[cnt].mid ) return Sum( l ,r ,cnt*2+1 );
    else
    {
       if( r <= tree[cnt].mid  ) return Sum( l , r , cnt * 2 );
       else return Sum( l  , tree[cnt].mid, cnt*2 )+Sum( tree[cnt].mid +1 , r ,cnt*2+1 );    
    }    
}
int main( )
{
    int Case,n,m,number,l,r,v;
    while( scanf( "%d",&Case )==1 )
    {
       for( int i=1; i<= Case ; i++ )
       {
          Tree e;
          scanf( "%d%d",&number,&m );
          e.Maketree(1 , number , 1);
          while( m -- )
          {
             scanf( "%d%d%d",&l,&r,&v );
             e.Change(l,r,v,1);    
          }        
          printf( "Case %d: The total value of the hook is %d.\n",i,e.Sum( 1,number, 1 ) );
       }    
    }
     return 0;    
}