poj 3667 Hotel(线段树)

poj 3667 Hotel

题目大意：给定一个区间，两种操作：

• 1 x：找到区间中最左边，将长度为x的区间放入，要求尽量靠左。
• 2 l r：清空l，r + l - 1这段区间。

解题思路：线段树的区间合并，每个节点记录S，L，R即可。

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

using namespace std;

const int maxn =50005;

int N, M;

#define lson(x) ((x)<<1)
#define rson(x) (((x)<<1)|1)
int lc[maxn << 2], rc[maxn << 2], V[maxn << 2];
int L[maxn << 2], R[maxn << 2], S[maxn << 2];

void maintain(int u, int v) {
    V[u] = v;
    int len = rc[u] - lc[u] + 1;
    L[u] = R[u] = S[u] = (v ? 0 : len);
}

void pushup (int u) {
    S[u] = max(max(S[lson(u)], S[rson(u)]), R[lson(u)] + L[rson(u)]);
    L[u] = L[lson(u)] + (L[lson(u)] == rc[lson(u)] - lc[lson(u)] + 1 ? L[rson(u)] : 0);
    R[u] = R[rson(u)] + (R[rson(u)] == rc[rson(u)] - lc[rson(u)] + 1 ? R[lson(u)] : 0);
}

void pushdown (int u) {
    if (V[u] != -1) {
        maintain(lson(u), V[u]);
        maintain(rson(u), V[u]);
        V[u] = -1;
    }
}

void build (int u, int l, int r) {
    lc[u] = l;
    rc[u] = r;
    V[u] = -1;

    if (l == r) {
        V[u] = 0;
        L[u] = R[u] = S[u] = 1;
        return;
    }

    int mid = (l + r) / 2;
    build(lson(u), l , mid);
    build(rson(u), mid + 1, r);
    pushup(u);
}

void modify (int u, int l, int r, int v) {
    if (l <= lc[u] && rc[u] <= r) {
        maintain(u, v);
        return;
    }

    pushdown(u);
    int mid = (lc[u] + rc[u]) / 2;
    if (l <= mid)
        modify(lson(u), l, r, v);
    if (r > mid)
        modify(rson(u), l, r, v);
    pushup(u);
}

int query (int u, int k) {
    if (S[u] < k)
        return 0;

    pushdown(u);
    int ret;

    if (S[lson(u)] >= k)
        ret = query(lson(u), k);
    else if (R[lson(u)] + L[rson(u)] >= k) {
        int mid = (lc[u] + rc[u]) / 2;
        ret = mid - R[lson(u)] + 1;
    } else
        ret = query(rson(u), k);
    pushup(u);
    return ret;
}

int main () {
    while (scanf("%d%d", &N, &M) == 2) {
        int x, l, r;
        build(1, 1, N);
        while (M--) {
            scanf("%d", &x);

            if (x == 1) {
                scanf("%d", &r);
                l = query(1, r);
                printf("%d\n", l);
                if (l)
                    modify(1, l, l + r - 1, 1);
            } else {
                scanf("%d%d", &l, &r);
                modify(1, l, l + r - 1, 0);
            }
        }
    }
    return 0;
}