Find out wheter segments AB CD intersect

segment_intersection.go

type point struct {
	x int
	y int
}

func pointSum(p1, p2 point) point {
	return point{
		x: p1.x + p2.x,
		y: p1.y + p2.y,
	}
}

type lineSegment struct {
	begin point
	end   point
}

func isCounterClockwiseListed(A, B, C point) bool {
	// 3 points are listed ccw iff slope AB < AC
	// Slope AB = (B_y-A_y)/(B_x-A_x)
	return (B.y-A.y)*(C.x-A.x) < (C.y-A.y)*(B.x-A.x)
}

func doSegmentsIntersect(s1, s2 lineSegment) bool {
	// 2 segments AB CD intersect iff A and B separated by CD & C and D separated by AB
	// if A and B separated by CD, then ACD and BCD should have different orientation

	A := s1.begin
	B := s1.end

	C := s2.begin
	D := s2.end
	return isCounterClockwiseListed(A, C, D) != isCounterClockwiseListed(B, C, D) &&
		isCounterClockwiseListed(A, B, C) != isCounterClockwiseListed(A, B, D)
}