POJ1269 考虑两直线 平行 or 共线 ？是否垂直于x轴？即sameline过程，非常关键 再叉积求交点即可 吐槽"%.2lf" 过不了，得用"%.2f"

gistfile1.cpp

#include <algorithm>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <utility>
#include <cstdio>
#include <string>
#include <ctime>
#include <cmath>
#include <stack>
#include <queue>
#include <list>
#include <map>
#include <set>

const double eps = 1e-6;

typedef long long int64;

struct point
{
   double x, y;
};
typedef point line;

int n;
point a[5];

int cmp_d(double x)
{
   if (std::abs(x) < eps) return 0;
   return x < 0 ? -1 : 1;
}

line operator - (point a, point b) { return (line) { a.x - b.x, a.y - b.y }; }
line operator + (point a, point b) { return (line) { a.x + b.x, a.y + b.y }; }
line operator * (point a, double lmd) { return (line) { a.x * lmd, a.y * lmd }; }
double cross(line a, line b) { return a.x * b.y - a.y * b.x; }

int sameline()
{
   if (cmp_d(cross(a[1] - a[2], a[3] - a[4])) == 0)
   {
      if (cmp_d(a[1].x - a[2].x) == 0 && cmp_d(a[3].x - a[4].x) == 0)
      {
         if (cmp_d(a[1].x - a[3].x) == 0) return 1;
         else return -1;
      }
      double k1 = (a[1].y - a[2].y) / (a[1].x - a[2].x);
      double b1 = a[1].y - k1 * a[1].x;
      if (cmp_d(a[3].x * k1 + b1 - a[3].y) == 0) return 1;
      else return -1;
   }
   return 0;
}

void intersection(point a, line v, point b, line w)
{
   line u = a - b;
   double t = cross(w, u) / cross(v, w);
   line aim = a + v * t;
   printf("POINT %.2f %.2f\n", aim.x, aim.y);
}

int main()
{
#ifndef ONLINE_JUDGE
   freopen("1269.in", "r", stdin);
   freopen("1269.out", "w", stdout);
#endif

   puts("INTERSECTING LINES OUTPUT");
   
   scanf("%d", &n);
   for (int i = 1; i <= n; ++i)
   {
      int b;
      for (int j = 1; j <= 4; ++j) scanf("%lf%lf", &a[j].x, &a[j].y);
      if ((b = sameline()) == 1) puts("LINE");
      else if (b == -1) puts("NONE");
      else intersection(a[1], a[1] - a[2], a[3], a[3] - a[4]);
   }

   puts("END OF OUTPUT");

   return 0;
}