文章标题

//Q pos 问包含pos的连续区间的长度
//D pos 删除pos位置的元素
//R 恢复上一个被删除的元素
//用栈维护被删除的元素位置
//用线段树维护左边连续区间，右边连续区间的长度
#include<cstdio>
#include<cstring>
#include<iostream>
#include<vector>
using namespace std ;
const int maxn = 500010 ;
#define left v<<1
#define right v<<1|1
struct node
{
    int l , r ;
    int ma_l , ma_r;
}tree[maxn<<2] ;
int stack[maxn] ;
void build(int l , int  r , int v)
{
    tree[v].l = l ;
    tree[v].r = r;
    tree[v].ma_l  = tree[v].ma_r  = r - l + 1 ;
    if(l == r)return ;
    int mid = (l + r) >> 1 ;
    build(l , mid , left) ;
    build(mid + 1 , r , right) ;
}
void push_up(int v)
{
    tree[v].ma_l = tree[left].ma_l ;
    tree[v].ma_r = tree[right].ma_r ;
    if(tree[v].ma_l == tree[left].r - tree[left].l + 1)
    tree[v].ma_l += tree[right].ma_l ;
    if(tree[v].ma_r == tree[right].r - tree[right].l + 1)
    tree[v].ma_r += tree[left].ma_r ;
}
int query(int v , int num)
{
    if(tree[v].l == tree[v].r)
    return tree[v].ma_l ;
    int mid = (tree[v].l + tree[v].r) >> 1 ;
    if(num <= mid)
    {
        if(tree[left].r - tree[left].ma_r + 1 <= num)
        return tree[left].ma_r + tree[right].ma_l;
        else return query(left , num) ;
    }
    else
    {
        if(tree[right].l + tree[right].ma_l - 1 >= num)
        return tree[left].ma_r + tree[right].ma_l;
        else return query(right ,num) ;
    }
}
void update(int pos , int op , int v)
{
    if(tree[v].l == tree[v].r)
    {
        tree[v].ma_l = tree[v].ma_r = op ;
        return ;
    }
    int mid = (tree[v].l + tree[v].r) >> 1 ;
    if(pos <= mid)
    update(pos , op , left);
    else update(pos , op , right) ;
    push_up(v) ;
}
int main()
{
   // freopen("in.txt" ,"r" , stdin) ;
    int n , m ;
    while(~scanf("%d%d" , &n , &m))
    {
        build(1 , n , 1) ;
        int pos ;
        int top = 0 ;
        char ch[10] ;
        while(m--)
        {
            scanf("%s" , ch) ;
            if(ch[0] == ‘D‘)
            {
                scanf("%d" , &pos) ;
                stack[++top] = pos ;
                update(pos , 0 , 1) ;
            }
            else if(ch[0] == ‘R‘)
            {
                if(!top)continue ;
                pos = stack[top--] ;
                update(pos , 1 , 1) ;
            }
            else
            {
                scanf("%d" , &pos) ;
                printf("%d\n" , query(1 , pos)) ;
            }
        }
    }
    return 0 ;
}