Poj 2318 TOYS (叉积+二分)

青旅半醒 2023-01-17 06:21 162阅读 0赞

好久没做计算几何了，随便找道题恢复下手感，明显感觉写复杂了。。。。

应该是最后一道用vc6.0敲的题了，下一道改用codeblocks

题意：给定一个长方形箱子，中间有n条线段，将其分为n+1个区域，给定m个玩具的坐标，统计每个区域中的玩具个数。

思路：二分枚举区域，玩具与分割线的位置用叉积判断

#include <cstdio>
    #include <cstring>
    
    const int N=5005;
    int n,m,x1,y11,x2,y2;
    int cnt[N];
    
    template<typename Type>
    class Point
    {
    public:
    	Type x,y;
    
    	Point(){}
    	Point (Type _x,Type _y)
    	{
    		x=_x;
    		y=_y;
    	}
    	Point operator-(const Point &b) const
    	{
    		return Point(x-b.x,y-b.y);
    	}
    	//调用点a的该函数
    	//返回正值点a在向量bc的左侧
    	//返回负值点a在向量bc的右侧
    	//返回0点a在向量bc这条直线上
    	Type Cross (Point b,Point c)
    	{return (b.x-x)*(c.y-y)-(c.x-x)*(b.y-y);}
    };
    
    Point<int> up[N],down[N],data[N];
    
    void Init ()
    {
    	int i,a,b;
    	memset(cnt,0,sizeof(cnt));
    	for (i=0;i<n;i++)
    	{
    		scanf("%d%d",&a,&b);
    		up[i]=Point<int>(a,y11);
    		down[i]=Point<int>(b,y2);
    	}
    	for (i=1;i<=m;i++)
    	{
    		scanf("%d%d",&a,&b);
    		data[i]=Point<int>(a,b);
    	}
    }
    
    int Solve (Point<int> cc)
    {
    	int low=0,high=n,mid;
    	while (low<=high)
    	{
    		mid=(low+high)>>1;
    		if (down[mid].Cross(up[mid],cc)>0)
    			high=mid-1;
    		else
    			low=mid+1;
    	}
    	if (low>n) low=n;
    	return low;
    }
    
    int main ()
    {
    #ifdef ONLINE_JUDGE
    #else
    	freopen("read.txt","r",stdin);
    #endif
    	while (~scanf("%d",&n),n)
    	{
    		scanf("%d%d%d%d%d",&m,&x1,&y11,&x2,&y2);
    		int i;
    		Init ();
    		for (i=1;i<=m;i++)
    			cnt[Solve(data[i])]++;
    		for (i=0;i<=n;i++)
    			printf("%d: %d\n",i,cnt[i]);
    		printf("\n");
    	}
    	return 0;
    }