CodeForces 46 D. Parking Lot

简单的区间合并线段树，不过要特殊讨论一下当前车是停车场里面唯一一辆车的情况还有车停在边界的情况

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;
#define lson rt<<1,l,mid
#define rson rt<<1|1,mid + 1,r
typedef long long LL;
const int maxn = 1e5 + 10;
const int maxm = 1e3;
int lmax[maxn << 2], rmax[maxn << 2], mmax[maxn << 2], lazy[maxn << 2];
int spos[maxm], epos[maxm];

void pushup(int rt, int l, int r) {
	int lc = rt << 1, rc = rt << 1 | 1, mid = (l + r) >> 1;
	int Llen = mid - l + 1, Rlen = r - mid;
	lmax[rt] = lmax[lc]; rmax[rt] = rmax[rc];
	mmax[rt] = max(mmax[lc], mmax[rc]);
	if (rmax[lc] != 0 && lmax[rc] != 0) {
		if (lmax[lc] == Llen) lmax[rt] += lmax[rc];
		if (rmax[rc] == Rlen) rmax[rt] += rmax[lc];
		mmax[rt] = max(mmax[rt], rmax[lc] + lmax[rc]);
		mmax[rt] = max(mmax[rt], max(lmax[rt], rmax[rt]));
	}
}

void pushdown(int rt, int l, int r) {
	if (lazy[rt] == -1) return;
	int lc = rt << 1, rc = rt << 1 | 1, mid = (l + r) >> 1;
	int Llen = mid - l + 1, Rlen = r - mid;
	lazy[lc] = lazy[rc] = lazy[rt];
	lmax[lc] = rmax[lc] = mmax[lc] = lazy[rt] ? 0 : Llen;
	lmax[rc] = rmax[rc] = mmax[rc] = lazy[rt] ? 0 : Rlen;
	lazy[rt] = -1;
}

void build(int rt, int l, int r) {
	if (l == r) {
		lmax[rt] = rmax[rt] = mmax[rt] = 1;
		lazy[rt] = -1;
	}
	else {
		int mid = (l + r) >> 1;
		build(lson); build(rson);
		lazy[rt] = -1;
		pushup(rt, l, r);
	}
}

void update(int rt, int l, int r, int ql, int qr, int Val) {
	if (ql <= l && qr >= r) {
		lazy[rt] = Val;
		lmax[rt] = rmax[rt] = mmax[rt] = Val ? 0 : r - l + 1;
	}
	else {
		pushdown(rt, l, r);
		int mid = (l + r) >> 1;
		if (ql <= mid) update(lson, ql, qr, Val);
		if (qr > mid) update(rson, ql, qr, Val);
		pushup(rt, l, r);
	}
}

int query(int rt, int l, int r, int D) {
	int mid = (l + r) >> 1;
	if (lmax[rt] >= D) return l;
	pushdown(rt, l, r);
	if (mmax[rt << 1] >= D) return query(lson, D);
	if (rmax[rt << 1] + lmax[rt << 1 | 1] >= D) return mid - rmax[rt << 1] + 1;
	return query(rson, D);
}

int N, b, f, M;

int main() {
	int cnt = 1, ccnt = 0;
	scanf("%d%d%d%d", &N, &b, &f, &M);
	build(1, 1, N);
	for (int i = 1; i <= M; i++) {
		int cmd, x; scanf("%d%d", &cmd, &x);
		if (cmd == 1) {
            int s,e,rt = 1;
            bool flag = false;
            if(ccnt == 0) {
                //如果当前没有车，可以不考虑空位的问题
                if(lmax[rt] >= x) {
                    s = 1; e = x; flag = true;
                }
            }
            else {
                //先尝试停在左边界上
                if(lmax[rt] >= x + f) {
                    s = 1; e = x; flag = true;
                }
                else if(mmax[rt] >= x + b + f) {
                    //尝试停在中间
                    int ret = query(1,1,N,x + b + f);
                    s = ret + b; e = ret + b + x - 1; flag = true;
                }
                else if(rmax[rt] >= x + b) {
                    //尝试停在最后边界
                    s = N - rmax[rt] + 1 + b; e = s + x - 1; flag = true;
                }
            }
            if(flag) {
                ccnt++;
                printf("%d\n",s - 1);
                update(1,1,N,s,e,1);
                spos[i] = s; epos[i] = e;
            }
            else puts("-1");
		}
		else  {
			update(1, 1, N, spos[x], epos[x], 0);
			ccnt--;
		}
	}
	return 0;
}