poj2318 - TOYS

                                  想看更多的解题报告: http://blog.csdn.net/wangjian8006/article/details/7870410
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题目大意:有一个矩形盒子,盒子里会有一些木块线段,并且这些线段是按照顺序给出的,有n条线段,把盒子分层了n+1个区域,然后有m个玩具,这m个玩具的坐标是已知的,问最后每个区域有多少个玩具

解题思路:因为线段是有序给出,所以不用排序,判断某个点在哪个区域,采用二分法,将某个点和线段的叉积来判断这个点是在线的左边或者右边,根据这个来二分找出区域

#include <iostream>
using namespace std;
#define _MAXL_ 5010

typedef struct{
	int x, y;
}POINT;

typedef struct{
	POINT first,second;
}LINE;

class CBox{
private:
	int nTop,nLeft,nRight,nButtom;
	int nCountLine;						//记录盒子里有多少条线
	LINE *pLine;						//记录线的信息
	int *pRange;						//记录区间中的玩具有多少个
	int Multi(POINT p1,POINT p2,POINT p0);			//叉积计算
public:
	CBox();
	virtual ~CBox();
	void SetBorder(int top,int left,int right,int buttom);		//设置盒子矩形坐标
	void AddLine(int first,int second);							//在盒子中增加一条线
	int GetRange(int val);								//得到某个区间中的玩具个数
	void SetToy(POINT toy);							//在盒子里放一个玩具
};

CBox::CBox(){
	nCountLine = 0;
	pLine = new LINE[_MAXL_];
	pRange = new int[_MAXL_];
	memset(pRange,0,sizeof(pRange)*_MAXL_);
}

CBox::~CBox(){
	delete []pLine;
	delete []pRange;
}

void CBox::SetBorder(int top,int left,int right,int buttom){
	nTop = top;
	nLeft = left;
	nRight = right;
	nButtom = buttom;
}

void CBox::AddLine(int topx,int buttomx){
	pLine[nCountLine].first.x = topx;
	pLine[nCountLine].first.y = nTop;
	pLine[nCountLine].second.x = buttomx;
	pLine[nCountLine].second.y = nButtom;
	nCountLine++;
}

int CBox::GetRange(int val){
	return pRange[val];
}

int CBox::Multi(POINT p1,POINT p2,POINT p0){
	 return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}

void CBox::SetToy(POINT toy){			//利用二分查找,查找出该点在哪个区间
	int l, r, mid;
	l=0,r=nCountLine-1;
	while (l < r){
		mid = (l+r)>>1;
		if (Multi(toy, pLine[mid].first, pLine[mid].second) > 0) l = mid + 1;
		else r = mid;
	}  
	if (Multi(toy, pLine[l].first, pLine[l].second) < 0) pRange[l]++;
	else pRange[l+1]++;
}

int main(){
	int i,fx,lx;
	POINT a,b;
	int n,m;
	while(cin>>n && n){
		cin>>m>>a.x>>a.y>>b.x>>b.y;
		CBox box;
		box.SetBorder(a.y,a.x,b.x,b.y);
		for(i = 0;i < n;i++){
			cin>>fx>>lx;
			box.AddLine(fx,lx);
		}

		for(i = 0;i < m;i++){
			cin>>a.x>>a.y;
			box.SetToy(a);
		}

		for(i = 0;i <= n;i++){
			cout<<i<<": "<<box.GetRange(i)<<endl;
		}
		cout<<endl;
	}
	return 0;
}


 

 

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