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/*
Challenge 101
TASK #2 � Origin-containing Triangle
Submitted by: Stuart Little
You are given three points in the plane, as a list of six co-ordinates:
A=(x1,y1), B=(x2,y2) and C=(x3,y3).
Write a script to find out if the triangle formed by the given three
co-ordinates contain origin (0,0).
Print 1 if found otherwise 0.
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
typedef struct Point {
double x, y;
} Point;
double sign(Point p1, Point p2, Point p3) {
return (p1.x - p3.x) * (p2.y - p3.y)
- (p2.x - p3.x) * (p1.y - p3.y);
}
int point_in_triangle(Point p0, Point p1, Point p2, Point p3) {
double d1 = sign(p0, p1, p2);
double d2 = sign(p0, p2, p3);
double d3 = sign(p0, p3, p1);
bool has_neg = (d1 < 0.0) || (d2 < 0.0) || (d3 < 0.0);
bool has_pos = (d1 > 0.0) || (d2 > 0.0) || (d3 > 0.0);
if (!(has_neg && has_pos))
return 1;
else
return 0;
}
int main(int argc, char* argv[]) {
if (argc != 7) {
fputs("Usage: ch-2 x1 y1 x2 y2 x3 y3", stderr);
exit(EXIT_FAILURE);
}
else {
Point p[3], p0;
for (int i = 0; i < 3; i++) {
p[i].x = atof(argv[i * 2 + 1]);
p[i].y = atof(argv[i * 2 + 2]);
}
p0.x = p0.y = 0.0;
printf("%d\n", point_in_triangle(p0, p[0], p[1], p[2]));
}
}
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