poj 1269 Intersecting Lines

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题意：给个n，然后n行数据，每行四个点，代表两条直线，求两条直线平行，或者重合，或者相交，相交的话求出交点
叉积求交点公式：黑书p357
这里写图片描述

#include <cstdio>#include <cstring>struct Point{    int x,y;};struct Line{    Point s,e;};Line line1,line2;int det(int x1, int y1, int x2, int y2){    return x1*y2 - x2*y1;}/****求ab和ac叉积****/int cross(Point a, Point b, Point c){    return det(b.x-a.x,b.y-a.y,c.x-a.x,c.y-a.y);}int area(Point a, Point b, Point c){    return cross(a,b,c);}int main(){    int n;    while(scanf("%d",&n) != EOF)    {        printf("INTERSECTING LINES OUTPUT\n");        for(int i = 0; i < n; ++i)        {            scanf("%d %d %d %d %d %d %d %d",&line1.s.x,&line1.s.y,&line1.e.x,&line1.e.y,&line2.s.x,&line2.s.y,&line2.e.x,&line2.e.y);//            line1.e.x-line1.s.x,line1.e.y-line1.s.y------>x1,y1//            line2.e.x-line2.s.x,line2.e.y-line2.s.y------>x2,y2            if((line1.e.x-line1.s.x)*(line2.e.y-line2.s.y) - (line1.e.y-line1.s.y)*(line2.e.x-line2.s.x) == 0)//共线，然后判断平行还是重合            {                if(cross(line1.s,line1.e,line2.s) == 0)                    printf("LINE\n");                else                    printf("NONE\n");            }            //肯定就有交点了            else            {                float s1 = area(line1.s,line1.e,line2.s)/2.0;                float s2 = area(line1.s,line1.e,line2.e)/2.0;                printf("POINT %.2f %.2f\n",(s1*line2.e.x-s2*line2.s.x)/(s1-s2),(s1*line2.e.y-s2*line2.s.y)/(s1-s2));            }        }        printf("END OF OUTPUT\n");    }    return 0;}

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