线段树(区间合并) POJ 3667 Hotel

/*
题意：输入 1 a:询问是不是有连续长度为a的空房间,有的话住进最左边
输入 2 a b:将[a,a+b-1]的房间清空
线段树(区间合并)：lsum[]统计从左端点起最长连续空房间数，rsum[]类似，sum[]统计区间最长连续的空房间数，
它有三种情况：1.纯粹是左端点起的房间数；2.纯粹是右端点的房间数；3.当从左(右)房间起都连续时，加上另一个子节点
从左(右)房间起的数，sum[]再求最大值更新维护。理解没错，表达能力不足
详细解释：http://www.cnblogs.com/scau20110726/archive/2013/05/07/3065418.html
*/
#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;

#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
const int MAXN = 5e4 + 10;
const int INF = 0x3f3f3f3f;
struct Segment_Tree {
int sum[MAXN<<2], lsum[MAXN<<2], rsum[MAXN<<2], cover[MAXN<<2];
void push_up(int rt, int len)    {
lsum[rt] = lsum[rt<<1];
rsum[rt] = rsum[rt<<1|1];
if (lsum[rt] == len - (len>>1)) lsum[rt] += lsum[rt<<1|1];
if (rsum[rt] == len>>1)   rsum[rt] += rsum[rt<<1];
sum[rt] = max (rsum[rt<<1] + lsum[rt<<1|1], max (sum[rt<<1], sum[rt<<1|1]));
}
void push_down(int rt, int len) {
if (cover[rt] != -1)    {
cover[rt<<1] = cover[rt<<1|1] = cover[rt];
sum[rt<<1] = lsum[rt<<1] = rsum[rt<<1] = cover[rt] ? 0 : len - (len>>1);
sum[rt<<1|1] = lsum[rt<<1|1] = rsum[rt<<1|1] = cover[rt] ? 0 : len >> 1;
cover[rt] = -1;
}
}
void build(int l, int r, int rt)    {
sum[rt] = lsum[rt] = rsum[rt] = r - l + 1;
cover[rt] = -1;
if (l == r) return ;
int mid = (l + r) >> 1;
build (lson);   build (rson);
}
void updata(int ql, int qr, int c, int l, int r, int rt)   {
if (ql <= l && r <= qr) {
sum[rt] = lsum[rt] = rsum[rt] = c ? 0 : (r - l + 1);
cover[rt] = c;  return ;
}
push_down (rt, r - l + 1);
int mid = (l + r) >> 1;
if (ql <= mid)  updata (ql, qr, c, lson);
if (qr > mid)   updata (ql, qr, c, rson);
push_up (rt, r - l + 1);
}
int query(int w, int l, int r, int rt) {
if (l == r) return l;
push_down (rt, r - l + 1);
int mid = (l + r) >> 1;
if (sum[rt<<1] >= w)    return query (w, lson);
else if (rsum[rt<<1] + lsum[rt<<1|1] >= w)  return mid - rsum[rt<<1] + 1;
else    return query (w, rson);
}
}st;

int main(void)  {       //POJ 3667 Hotel
int n, m;
while (scanf ("%d%d", &n, &m) == 2) {
st.build (1, n, 1);
for (int i=1; i<=m; ++i)    {
int op, a, b; scanf ("%d%d", &op, &a);
if (op == 1)    {
if (st.sum[1] < a)  puts ("0");
else    {
int p = st.query (a, 1, n, 1);
printf ("%d\n", p);
st.updata (p, p + a - 1, 1, 1, n, 1);
}
}
else    {
scanf ("%d", &b);
st.updata (a, a + b - 1, 0, 1, n, 1);
}
}
}

return 0;
}