HDU2795 Billboard【线段树 点修改+区间查询】

Billboard

http://acm.hdu.edu.cn/showproblem.php?pid=2795

Time Limit: 20000/8000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 30888    Accepted Submission(s): 12391

Problem Description

At the entrance to the university, there is a huge rectangular billboard of size h*w (h is its height and w is its width). The board is the place where all possible announcements are posted: nearest programming competitions, changes in the dining room menu, and other important information.

On September 1, the billboard was empty. One by one, the announcements started being put on the billboard.

Each announcement is a stripe of paper of unit height. More specifically, the i-th announcement is a rectangle of size 1 * wi.

When someone puts a new announcement on the billboard, she would always choose the topmost possible position for the announcement. Among all possible topmost positions she would always choose the leftmost one.

If there is no valid location for a new announcement, it is not put on the billboard (that's why some programming contests have no participants from this university).

Given the sizes of the billboard and the announcements, your task is to find the numbers of rows in which the announcements are placed.

 

Input

There are multiple cases (no more than 40 cases).

The first line of the input file contains three integer numbers, h, w, and n (1 <= h,w <= 10^9; 1 <= n <= 200,000) - the dimensions of the billboard and the number of announcements.

Each of the next n lines contains an integer number wi (1 <= wi <= 10^9) - the width of i-th announcement.

 

Output

For each announcement (in the order they are given in the input file) output one number - the number of the row in which this announcement is placed. Rows are numbered from 1 to h, starting with the top row. If an announcement can't be put on the billboard, output "-1" for this announcement.

 

 

Sample Input

3 5 5
2
4
3
3
3

 Sample Output

1
2
1
3
-1

Author

hhanger@zju

 

Source

HDOJ 2009 Summer Exercise（5）

 

题意

一个h*w的公告牌，要在其上贴公告。输入的是1*wi的wi值，这些是公告的尺寸。接下来要满足的条件有：

1、尽量往上，同一高度尽量靠左。

2、求第n个广告所在的行数。(行数从1开始编号)

3、没有合适的位置贴了则输出-1。

思路

查询并更新数列中第一个大于等于wi的值，并使其值减去wi，线段树单点更新。

C++代码

#include
#include

using namespace std;

#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1

const int N=200000;

int maxv[N<<2],w;

void pushup(int rt)
{
	maxv[rt]=max(maxv[rt<<1],maxv[rt<<1|1]);
}

void build(int l,int r,int rt)
{
	if(l==r)
	{
		maxv[rt]=w;
		return;
	}
	int m=(l+r)>>1;
	build(ls);
	build(rs);
	pushup(rt);
}

int update(int width,int l,int r,int rt)
{
	if(width>maxv[rt]) return -1;
	if(l==r)
	{
		maxv[rt]-=width;//将宽度为width的公告贴在的l行，第l行的剩余的长度要减去width 
		return l;//返回行号 
	}
	int m=(l+r)>>1,res;
	if(width<=maxv[rt<<1])
	  res=update(width,ls);
	else
	  res=update(width,rs);
	pushup(rt);
	return res;
}

int main()
{
	int h,n;
	while(~scanf("%d%d%d",&h,&w,&n))
	{
		int num=min(h,N),width;
		build(1,num,1);
		while(n--)
		{
			scanf("%d",&width);
			printf("%d\n",update(width,1,num,1));
		}
	}
	return 0;
}