hdu 1540 线段树+区间合并

每个线段维护左起连续长度，和右起连续长度，然后每次查询时讨论x所在连续段是否同时存在两个子段中，分类讨论即可

#include <iostream>
#include <cstring>
#include <algorithm>
#include <cstdio>
#include <stack>
#define MAX 50007

using namespace std;

int n,m,a;
char s[5];
stack<int> stk;

struct Tree
{
    int l , r , llen , rlen;
}tree[MAX<<2];

void build ( int u , int l , int r )
{
    tree[u].l = l , tree[u].r = r;
    tree[u].llen = tree[u].rlen = r-l+1;
    if ( l == r ) return;
    int mid = l + r >> 1;
    build ( u<<1 , l , mid );
    build ( u<<1|1 , mid+1 , r );
}

void push_up ( int u )
{
    tree[u].llen = tree[u<<1].llen;
    tree[u].rlen = tree[u<<1|1].rlen;
    if ( tree[u<<1].llen == tree[u<<1].r - tree[u<<1].l + 1 )
       tree[u].llen = tree[u<<1].llen + tree[u<<1|1].llen;
    if ( tree[u<<1|1].rlen == tree[u<<1|1].r - tree[u<<1|1].l + 1 )
       tree[u].rlen = tree[u<<1].rlen + tree[u<<1|1].rlen;         
}

void update ( int u , int x , int v)
{
    int l = tree[u].l , r = tree[u].r;
    if ( l == r )
    {
        tree[u].llen =  tree[u].rlen = v;
        return;
    }
    int mid = l + r >> 1;
    if ( x > mid ) update ( u<<1|1 , x , v );
    else update ( u<<1 , x , v );
    push_up ( u );
}

int query ( int u , int x )
{
    int l = tree[u].l , r = tree[u].r;
    if ( r-l+1 == tree[u].llen )
        return r-l+1;
    if ( l == r )
        return tree[u].llen;
    int mid = l + r >> 1;
    if ( x > mid )
    {
        if ( tree[u<<1|1].l + tree[u<<1|1].llen > x )
           return query ( u<<1|1 , x ) + tree[u<<1].rlen; 
        else return query ( u<<1|1 , x ); 
    }
    else
    {
        if ( tree[u<<1].r - tree[u<<1].rlen < x ) 
           return query ( u<<1 , x ) + tree[u<<1|1].llen;
        else return query ( u<<1 , x );
    }
}

int main ( )
{
    while ( ~scanf ( "%d%d" , &n , &m ) )
    {
        build ( 1 , 1 , n );
        while ( !stk.empty() ) stk.pop();
        for ( int i = 0 ; i < m ; i++ )
        {
            scanf ( "%s" , s );
            if ( s[0] == 'D' )
            {
                scanf ( "%d" , &a );
                update ( 1 , a , 0 );
                stk.push ( a );
            }
            else if ( s[0] == 'Q' )
            {
                scanf ( "%d" , &a );
                printf ( "%d\n" , query ( 1 , a ) );
            }
            else
            {
                update ( 1 , stk.top() , 1 );
                stk.pop ( );
            }
        }   
    }
}