POJ 2653 Pick-up sticks

考察点在于如何判断两线段相交（快速排斥+跨立），之前使用链表结构超时了，后来用vector实现。

 

判断线段相交的办法，这篇文章讲的很明白。http://324012406.iteye.com/blog/738318

 

#include <iostream>
#include <vector>

using namespace std;

typedef struct Coordinate
{
    Coordinate(double _x, double _y)
        :x(_x),y(_y)
    {
    }

    double x;
    double y;
} Coordinate;

typedef struct Stick
{
    Stick()
        :index(0),start(0.0,0.0),end(0.0,0.0)
    {
    }

    Stick(int i, double x1, double y1, double x2, double y2)
        :index(i),start(x1,y1),end(x2,y2)
    {
    }

    int index;
    Coordinate start;
    Coordinate end;
} Stick;


inline bool isRectCrossed(const Stick& s1,const Stick& s2)
{
    // rect1 
    double rect1_min_x = min(s1.start.x,s1.end.x);
    double rect1_max_x = max(s1.start.x,s1.end.x);
    double rect1_min_y = min(s1.start.y,s1.end.y);
    double rect1_max_y = max(s1.start.y,s2.end.y);

    // rect2
    double rect2_min_x = min(s2.start.x,s2.end.x);
    double rect2_max_x = max(s2.start.x,s2.end.x);
    double rect2_min_y = min(s2.start.y,s2.end.y);
    double rect2_max_y = max(s2.start.y,s2.end.y);

    // innerRect of rect1 and rect2
    double innerRect_min_x = max(rect1_min_x,rect2_min_x);
    double innerRect_max_x = min(rect1_max_x,rect2_max_x);
    
    if(innerRect_min_x > innerRect_max_x)
        return false;

    double innerRect_min_y = max(rect1_min_y,rect2_min_y);
    double innerRect_max_y = min(rect1_max_y,rect2_max_y);

    if(innerRect_min_y > innerRect_max_y)
        return false;
    
    return true;
}

inline double CrossProduct(const Coordinate& c1,const Coordinate& c2)
{
    return c1.x*c2.y-c2.x*c1.y;
}

inline bool isCrossed(const Stick& s1,const Stick& s2)
{
    if(!isRectCrossed(s1,s2))
        return false;

    if(CrossProduct(Coordinate(s1.start.x-s2.start.x,s1.start.y-s2.start.y),Coordinate(s2.end.x-s2.start.x,s2.end.y-s2.start.y))*CrossProduct(Coordinate(s2.end.x-s2.start.x,s2.end.y-s2.start.y),Coordinate(s1.end.x-s2.start.x,s1.end.y-s2.start.y))>=0 &&
       CrossProduct(Coordinate(s2.start.x-s1.start.x,s2.start.y-s1.start.y),Coordinate(s1.end.x-s1.start.x,s1.end.y-s1.start.y))*CrossProduct(Coordinate(s1.end.x-s1.start.x,s1.end.y-s1.start.y),Coordinate(s2.end.x-s1.start.x,s2.end.y-s1.start.y))>=0 ) 
        return true;

    return false;
}


int main()
{
    vector<Stick> vecStick;
    vecStick.push_back(Stick()); //Not use the first one.
    while(1)
    {
        int n = 0;
        scanf("%d",&n);

        if(n == 0)
            break;

        for(int i =1; i<=n; i++)
        {
            double x1,y1,x2,y2;
            scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);

            vecStick.push_back(Stick(i,x1,y1,x2,y2));
        }

        bool firstFlag = true;
        for(int i =1; i<n; i++)
        {
            bool crossed = false;
            for(int j = i+1; j<=n; j++)
            {
                if(isCrossed(vecStick[i],vecStick[j]))
                {
                    crossed = true;
                    break;
                }
            }

            if(!crossed)
            {
                if(firstFlag)
                {
                    printf("Top sticks: %d",i);
                    firstFlag = false;
                }
                else
                {
                    printf(", %d",i);
                }   
            }
        }

        printf(", %d.\n",n);   
        vecStick.clear();
        vecStick.push_back(Stick()); //Not use the first one.
    }

    return 0;
}