洛谷 P2894 [USACO08FEB]酒店Hotel 解题报告

P2894 [USACO08FEB]酒店Hotel

题目描述

The cows are journeying north to Thunder Bay in Canada to gain cultural enrichment and enjoy a vacation on the sunny shores of Lake Superior. Bessie, ever the competent travel agent, has named the Bullmoose Hotel on famed Cumberland Street as their vacation residence. This immense hotel has N (1 ≤ N ≤ 50,000) rooms all located on the same side of an extremely long hallway (all the better to see the lake, of course).

The cows and other visitors arrive in groups of size Di (1 ≤ Di ≤ N) and approach the front desk to check in. Each group i requests a set of Di contiguous rooms from Canmuu, the moose staffing the counter. He assigns them some set of consecutive room numbers r..r+Di-1 if they are available or, if no contiguous set of rooms is available, politely suggests alternate lodging. Canmuu always chooses the value of r to be the smallest possible.

Visitors also depart the hotel from groups of contiguous rooms. Checkout i has the parameters Xi and Di which specify the vacating of rooms Xi ..Xi +Di-1 (1 ≤ Xi ≤ N-Di+1). Some (or all) of those rooms might be empty before the checkout.

Your job is to assist Canmuu by processing M (1 ≤ M < 50,000) checkin/checkout requests. The hotel is initially unoccupied.

参考样例，第一行输入n，m ，n代表有n个房间，编号为1---n，开始都为空房，m表示以下有m行操作，以下 每行先输入一个数 i ，表示一种操作：

若i为1，表示查询房间，再输入一个数x，表示在1--n 房间中找到长度为x的连续空房并入住，输出连续x个房间中左端的房间号，尽量让这个房间号最小，若找不到长度为x的连续空房，输出0。

若i为2，表示退房，再输入两个数 x，y 代表 房间号 x---x+y-1 退房，即让房间为空。

输入输出格式

输入格式：

• Line 1: Two space-separated integers: N and M

• Lines 2..M+1: Line i+1 contains request expressed as one of two possible formats: (a) Two space separated integers representing a check-in request: 1 and Di (b) Three space-separated integers representing a check-out: 2, Xi, and Di

输出格式：

• Lines 1.....: For each check-in request, output a single line with a single integer r, the first room in the contiguous sequence of rooms to be occupied. If the request cannot be satisfied, output 0.

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线段树维护 区间最长0，离左端点的0个数，离右端点0的个数，就可以快速合并啦

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Code:

#include <cstdio>
#include <cstring>
#define ls id<<1
#define rs id<<1|1
int max(int x,int y){return x>y?x:y;}
const int N=1e5+10;
int lcnt[N<<2],rcnt[N<<2],len[N<<2],lazy[N<<2],n,m;
void updata(int id,int l,int r)
{
    int mid=l+r>>1,lenl=mid+1-l,lenr=r-mid;
    lcnt[id]=lcnt[ls];
    if(lcnt[ls]==lenl) lcnt[id]=max(lcnt[ls],lenl+lcnt[rs]);
    rcnt[id]=rcnt[rs];
    if(rcnt[rs]==lenr) rcnt[id]=max(rcnt[rs],lenr+rcnt[ls]);
    len[id]=max(rcnt[ls]+lcnt[rs],max(len[ls],len[rs]));
}
void push_down(int id,int l,int r)
{
    if(~lazy[id])
    {
        int mid=l+r>>1,lenl=mid+1-l,lenr=r-mid;
        lcnt[ls]=rcnt[ls]=len[ls]=(!lazy[id])*lenl;
        lcnt[rs]=rcnt[rs]=len[rs]=(!lazy[id])*lenr;
        lazy[ls]=lazy[rs]=lazy[id];
        lazy[id]=-1;
    }
}
void change(int id,int l,int r,int L,int R,int c)
{
    if(L!=R) push_down(id,L,R);
    if(l==L&&r==R)
    {
        lcnt[id]=rcnt[id]=len[id]=(!c)*(r+1-l);
        lazy[id]=c;
        return;
    }
    int Mid=L+R>>1;
    if(r<=Mid) change(ls,l,r,L,Mid,c);
    else if(l>Mid) change(rs,l,r,Mid+1,R,c);
    else change(ls,l,Mid,L,Mid,c),change(rs,Mid+1,r,Mid+1,R,c);
    updata(id,L,R);
}
int query(int id,int l,int r,int x)
{
    if(l==r) return l;
    push_down(id,l,r);
    int mid=l+r>>1;
    if(len[ls]>=x) return query(ls,l,mid,x);
    else if(rcnt[ls]+lcnt[rs]>=x) return mid+1-rcnt[ls];
    else return query(rs,mid+1,r,x);
}
int main()
{
    scanf("%d%d",&n,&m);
    memset(lazy,-1,sizeof(lazy));
    lcnt[1]=rcnt[1]=len[1]=n,lazy[1]=0;
    for(int op,x,y,i=1;i<=m;i++)
    {
        scanf("%d%d",&op,&x);
        if(op==1)
        {
            if(len[1]<x) printf("0\n");
            else
            {
                int pos;
                printf("%d\n",pos=query(1,1,n,x));
                change(1,pos,pos+x-1,1,n,1);
            }
        }
        else
            scanf("%d",&y),change(1,x,x+y-1,1,n,0);
    }
    return 0;
}

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2018.8.30