poj3667 线段树（区间合并）

题意：有编号为1~n的n个房间，有两种询问

          1.有人来订连续的k间房，有的话返回第一间房的编号，否则返回0。

          2.有人退连续的从a开始的连续的k间房。

解法：与之前做过的poj2750（线段树+动态规划）类似，就是在线段树上，记录每个区间的3个信息

          1.该区间最大的连续空房数

          2.该区间从最左边起的最大的连续空房数

          3.该区间从最右边起的最大的连续空房数

根据以上三个信息，每个非叶结点的信息都可以由它的左右儿子更新得到了。

#include <iostream>#include <cstdio>#include <cstring>#include <cmath>using namespace std;#define MAXN 50005int total[MAXN<<2], col[MAXN<<2], lsum[MAXN<<2], rsum[MAXN<<2];void PushUp(int l, int r, int rt) {    int m = (l + r) >> 1, lson = rt<<1, rson = rt<<1|1;    total[rt] = max(lsum[rson]+rsum[lson], max(total[lson], total[rson]));    if (lsum[lson] == m - l + 1) lsum[rt] = lsum[lson] + lsum[rson];    else lsum[rt] = lsum[lson];    if (rsum[rson] == r - m) rsum[rt] = rsum[rson] + rsum[lson];    else rsum[rt] = rsum[rson];}void PushDown(int l, int r, int rt){    int m = (l + r) >> 1, lson = rt << 1, rson = rt<<1|1;    total[lson] = lsum[lson] = rsum[lson] = (col[rt] == 1 ? m - l + 1 : 0);    total[rson] = lsum[rson] = rsum[rson] = (col[rt] == 1 ? r - m : 0);    col[lson] = col[rson] = col[rt];    col[rt] = 0;}void Build(int l, int r, int rt) {    lsum[rt] = rsum[rt] = total[rt] = r - l + 1;    if (l == r) return;    int m = (l + r) >> 1;    Build(l, m, rt<<1);    Build(m+1, r, rt<<1|1);}void Update(int L, int R, int c, int l, int r, int rt) {    if (l >= L && r <= R) {       col[rt] = c;       total[rt] = lsum[rt] = rsum[rt] = (c == 1 ? r - l + 1 : 0);       return;    }    if (col[rt]) PushDown(l, r, rt);    int m = (l + r) >> 1;    if (m >= L) Update(L, R, c, l, m, rt<<1);    if (m < R) Update(L, R, c, m+1, r, rt<<1|1);    PushUp(l, r, rt);}int Query(int l, int r, int rt, int c) {    if (total[rt] < c) return 0;    if (l == r) return l;    if (col[rt]) PushDown(l, r, rt);    int m = (l + r) >> 1, lson = rt<<1, rson = rt<<1|1;    if (total[lson] >= c) return Query(l, m, lson, c);    else if (rsum[lson]+lsum[rson] >= c) return m - rsum[lson] + 1;    else return Query(m+1, r, rson, c);}int main(){    int n, m, op, a, b;    scanf ("%d%d", &n, &m);    memset(col, 0, sizeof (col));    Build(1, n, 1);    while (m--) {        scanf ("%d", &op);        if (op == 1) {            scanf ("%d", &a);            int res = Query(1, n, 1, a);            printf ("%d\n", res);            if (res) Update(res, res+a-1, -1, 1, n, 1);        }        else {            scanf ("%d %d", &a, &b);            Update(a, a+b-1, 1, 1, n, 1);        }    }    return 0;}