poj 1269 题解

求直线交点，直接上代码。

#include<cmath>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

struct point{
    int x,y;
    point (){}
    point (int a,int b): x(a),y(b){}
    friend point operator + (const point &a,const point &b){
        return point(a.x+b.x,a.y+b.y);
    }

    friend point operator - (const point &a,const point &b){
        return point(a.x-b.x,a.y-b.y);
    }

    friend point operator * (const int &r,const point &a){
        return point(r*a.x,r*a.y);
    }

};

inline int det(point a,point b) {return a.x*b.y-a.y*b.x;}
inline int dot(point a,point b) {return a.x*b.x+a.y*b.y;}

inline bool On (point p,point s,point t){
    return det(p-s,t-s)==0;
}

inline bool parallel(point a,point b,point c,point d){return det(a-b,c-d)==0;}

inline void line_make_point(point s1,point t1,point s2,point t2) //逻辑上必须先判断parallel
{
    double a1=det(s1-s2,t2-s2);
    double a2=det(t1-s2,t2-s2);
    printf("POINT %.2f %.2f
",1/(a1-a2)*(a1*t1.x-a2*s1.x),1/(a1-a2)*(a1*t1.y-a2*s1.y));
}
int t;
point s1,t1,s2,t2,ans;
int x,y;
int main()
{
    scanf("%d",&t);
    printf("INTERSECTING LINES OUTPUT
");
    while (t--)
    {
        scanf("%d%d",&x,&y);s1=point(x,y);
        scanf("%d%d",&x,&y);t1=point(x,y);
        scanf("%d%d",&x,&y);s2=point(x,y);
        scanf("%d%d",&x,&y);t2=point(x,y);
        if (parallel(s1,t1,s2,t2))
            {
                if (On(s1,s2,t2))
                    printf("LINE
");
                        else printf("NONE
");
                continue;
            }
        else {
            line_make_point(s1,t1,s2,t2);
        }
    }
    printf("END OF OUTPUT
");
    return 0;
}