POJ1269 直线相交

版子 http://blog.csdn.net/acm_zl/article/details/9471451

    #include <iostream>
    #include <cstdio>
    #include <string>
    #include <string.h>
    #include <map>
    #include <vector>
    #include <cstdlib>
    #include <cmath>
    #include <algorithm>
    #include <queue>
    #include <set>
    #include <stack>
    using namespace std;  

    int main()
    {
        int t;
        double x1,y1,x2,y2,x3,y3,x4,y4;
        scanf("%d", &t);
        printf("INTERSECTING LINES OUTPUT\n");
        while(t--)
        {
            scanf("%lf%lf%lf%lf%lf%lf%lf%lf", &x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4);
            if(x1==x2 && x3==x4)//两直线都没有斜率
            {
                if(x3==x1)
                    printf("LINE\n");
                else
                    printf("NONE\n");
            }
            else if(x1==x2 && x3!=x4)//有一条直线斜率存在
            {
                double k = (y4-y3)*1.0/(x4-x3);
                double b = y3-(k*x3);
                double ansx = x1;
                double ansy = k*x1+b;
                printf("POINT %.2lf %.2lf\n", ansx, ansy);
            }
            else if(x1!=x2 && x3==x4)//有一条直线斜率存在
            {
                double k = (y2-y1)*1.0/(x2-x1);
                double b = y2-(k*x2);
                double ansx = x3;
                double ansy = k*x3+b;
                printf("POINT %.2lf %.2lf\n", ansx, ansy);
            }
            else //两条直线斜率都存在
            {
                double k1 = (y2-y1)*1.0/(x2-x1);
                double b1 = y2-(k1*x2);
                double k2 = (y4-y3)*1.0/(x4-x3);
                double b2 = y3-(k2*x3);
                if(k1==k2)
                {
                    if(b1==b2)
                        printf("LINE\n");
                    else
                        printf("NONE\n");
                }
                else
                {
                    double ansx = (b1-b2)*1.0/(k2-k1);
                    double ansy = k1*ansx + b1;
                    printf("POINT %.2lf %.2lf\n", ansx, ansy);
                }
            }
        }
        printf("END OF OUTPUT\n");
        return 0;
    }