Poj 2318 TOYS (叉积+二分)-蒲公英云

Poj 2318 TOYS (叉积+二分)

青旅半醒 2023-01-17 06:21 259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;
}