POJ 3667 Hotel 线段树 区间合并 入门题

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
#define maxn 50003
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define mid int m = (l + r)>>1
int col[maxn<<2];
int lsum[maxn<<2], msum[maxn<<2], rsum[maxn<<2];
int n, m;
int max(int a , int b) { return a > b ? a : b; } 

void pushup(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];
    msum[rt] = max(rsum[rt<<1] + lsum[rt<<1|1],  max(msum[rt<<1], msum[rt<<1|1]) );
}

void pushdown(int rt, int len)
{
    if(col[rt] != -1)
    {
        col[rt<<1] = col[rt<<1|1] = col[rt];
        lsum[rt<<1] = rsum[rt<<1] = msum[rt<<1] = col[rt] ? 0 :(len - (len >>1));
        lsum[rt<<1|1] = rsum[rt<<1|1] = msum[rt<<1|1] = col[rt] ? 0 : (len>>1) ;
        col[rt] = -1;
    }
}

void build(int l, int r, int rt)
{
    lsum[rt] = msum[rt] = rsum[rt] = r-l+1;
    col[rt] = -1;
    if(l == r)
        return;
    mid;
    build(lson);
    build(rson);
}

void update(int L, int R, int v, int l, int r, int rt)
{
    if(L <= l && r <= R )
    {
        col[rt] = v;
        lsum[rt] = msum[rt] = rsum[rt] = v ? 0 : (r-l+1);
        return;
    }
    pushdown(rt, r-l+1);
    mid;
    if(L <= m) update(L, R, v, lson);
    if(R > m) update(L, R, v, rson);
    pushup(rt, r-l+1);
}
int query(int v, int l, int r, int rt)
{
    if(l == r) return l;
    pushdown(rt, r-l+1);
    mid;
    if(msum[rt<<1] >= v) return query(v, lson);
    else if( rsum[rt<<1] + lsum[rt<<1|1] >= v) 
        return m - rsum[rt<<1] + 1;
    else
        return query(v, rson);
}
int main()
{
    int i, j;
    while( ~scanf("%d%d", &n, &m))
    {
        int op, x, y;
        build(1, n, 1);
        while(m--)
        {
            scanf("%d%d", &op, &x);
            if(op == 1)
            {
                if(msum[1] < x) 
                    puts("0");
                else 
                {
                    int k = query(x, 1, n, 1);
                    printf("%d\n", k);
                    update(k , k+x-1, 1, 1, n, 1);
                }
            }
            else
            {
                scanf("%d", &y);
                update(x, x+y-1, 0, 1, n, 1);
            }
        }
    }
    return 0;
}