HDU 1754 I Hate It

这是一道简单的入门的线段树的题目：

#include<cstdio>
#include<iostream>
#include<cstdlib>
using namespace std;
class Node
{
public:
      int l,r,mid;
      int max,count;
};
Node tree[800024];
int num[200024];
class Tree
{
public:
     int Max( int a,int b )
     { return a>b?a:b; }
     int Qestion( int l,int r,int cnt );
     void Maketree( int l,int r,int cnt );
     void Change( int n,int m,int cnt );
};
void Tree::Change( int n,int m,int cnt )
{
    tree[cnt].max =Max(tree[cnt].max,m);
    if( tree[cnt].l==n&&tree[cnt].r==n )
    {
         tree[cnt].count =tree[cnt].max= m; 
         return;
    }
    else
    {
        if( n > tree[cnt].mid )
           Change( n,m,cnt*2+1 );
        else Change( n , m ,cnt*2 );
    }    
}
void Tree::Maketree(int l,int r,int cnt)
{
   if( l == r )
   {
      tree[cnt].l=tree[cnt].r=tree[cnt].mid=l;
      tree[cnt].count=num[l];
      tree[cnt].max = num[l];    
         
      return ;
   }
   else
   {
      tree[cnt].mid = ( l+r )>>1;
      tree[cnt].l = l;
      tree[cnt].r = r;
      Maketree( l , tree[cnt].mid ,cnt*2 );
      Maketree( tree[cnt].mid +1 , r, cnt*2+1 );
      tree[cnt].max = Max( tree[cnt*2].max , tree[cnt*2+1].max ) ;        
   }    
}
int Tree::Qestion(int l,int r,int cnt)
{
       if( tree[cnt].l==l&&tree[cnt].r==r )
       { 
        return tree[cnt].max;        
    }
    else
    {
        if( l>tree[cnt].mid )
           return  Qestion( l , r , cnt*2+1 );
        else if( r <= tree[cnt].mid )
             return Qestion( l , r , cnt*2 );
       else
          return Max(Qestion( l , tree[cnt].mid , cnt*2 ),Qestion( tree[cnt].mid+1 , r , cnt*2+1 ));
    }
}
int main( )
{
    int n,m,l,r;
    char c[10];
    while( scanf( "%d%d",&n,&m )==2 )
    {
        Tree e;
       for( int i=1; i<= n; i++ )
           scanf( "%d",&num[i] );
        e.Maketree( 1 , n ,1 );
       for( int i=1; i<=m; i++ )
       {
            scanf( "%s%d%d",c , &l ,&r );
            if( c[0]=='Q' )
             printf( "%d\n",e.Qestion( l,r,1 ) );
            else e.Change( l ,r, 1 );        
       }    
    }
    return 0;    
}