【codevs 1369】题解

#include <iostream>
#include <stdio.h>

using namespace std;

int n , m;
int a[200000 + 2];
int i;
int l , r;

struct Node
{
int l , r;
int value;
Node * left , * right;
};

int merge( int a , int b )
{
return a + b;
}

void modify( int x , Node * cur )
{
if( cur -> l == cur -> r )
{
cur -> value = 0;
return;
}
int mid = ( cur -> l + cur -> r ) / 2;
if( x > mid )
modify( x , cur -> right );
else
modify( x , cur -> left );
cur -> value = merge( cur -> left -> value , cur -> right -> value );
return;
}

int find( int l , int r , Node * cur )
{
if( cur -> l == l && cur -> r == r )
return cur -> value;
int mid = ( cur -> l + cur -> r ) / 2;
if( l > mid )
return find( l , r , cur -> right );
else if( mid >= r )
return find( l , r , cur -> left );
else
return merge( find( l , mid , cur -> left ) , find( mid + 1 , r , cur -> right ) );
}

Node * build( int l , int r )
{
Node * cur = new Node();
cur -> l = l;
cur -> r = r;
if( cur -> l == cur -> r )
{
cur -> value = a[l];
return cur;
}
int mid = ( cur -> l + cur -> r ) / 2;
cur -> left = build( l , mid );
cur -> right = build( mid + 1 , r );
cur -> value = merge( cur -> left -> value , cur -> right -> value );
return cur;
}

Node * root;

int main()
{
scanf( "%d" , &n );
for( i = 1 ; i <= n ; i++ )
scanf( "%d" , &a[i] );
root = build( 1 , n );
scanf( "%d" , &m );
for( i = 0 ; i < m ; i++ )
{
scanf( "%d %d" , &l , &r );
printf( "%.2f\n" , 3.14 * find( l , r , root ) );
modify( ( l + r ) / 2 , root );
}
return 0;
}