HDU2795 Billboard【线段树点修改+区间查询】

公告牌公告张贴问题的线段树解法

最新推荐文章于 2019-11-27 18:57:57 发布

原创最新推荐文章于 2019-11-27 18:57:57 发布 · 221 阅读

0 ·

CC 4.0 BY-SA版权

数据结构专栏收录该内容

118 篇文章

订阅专栏

博客围绕一个h*w的公告牌张贴公告问题展开。公告为1*wi的尺寸，需尽量往上、同一高度尽量靠左张贴。要找出第n个广告所在行数，无合适位置则输出 -1。解题思路是查询并更新数列中首个大于等于wi的值，用线段树单点更新，还给出了C++代码。

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

Sample Output

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<iostream>
#include<algorithm>

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;
}