might be making a mistake starting 2018...

2019/day10/part2/trig/trig.go

@@ -0,0 +1,45 @@
+package trig
+
+import "math"
+
+/*
+AngleOffVertical takes in two 2D points, it calculates the angle
+between the line and a vertical line (straight up from origin)
+NOTE: "up"/"top" and "down" are lexically flipped b/c of drawing a grid
+where 0, 0 is the top left corner and higher numbers physically go DOWN
+but lexically increase/go UP 🤦‍♂️
+*/
+func AngleOffVertical(startX, startY, endX, endY int) float64 {
+	rise := float64(endX) - float64(startX)
+	run := float64(endY) - float64(startY)
+
+	var angle float64
+	// basically a big if/elseif/else block
+	switch {
+	case run == 0 && rise < 0: // up
+		angle = 0
+	case run == 0 && rise > 0: // down
+		angle = 180
+	case rise == 0 && run < 0: // left
+		angle = 270
+	case rise == 0 && run > 0: // right
+		angle = 90
+	case rise < 0 && run > 0: // top right
+		angle = -1 * math.Atan(run/rise) * 180 / math.Pi
+	case rise > 0 && run > 0: // bottom right
+		angle = 90 + math.Atan(rise/run)*180/math.Pi
+	case rise > 0 && run < 0: // bottom left
+		angle = 180 + -1*math.Atan(run/rise)*180/math.Pi
+	case rise < 0 && run < 0: // top left
+		angle = 270 + math.Atan(rise/run)*180/math.Pi
+	}
+
+	return angle
+}
+
+// Distance calculates the distance between two sets of 2D coordinates via Pythagorean's theorem
+func Distance(startX, startY, endX, endY int) float64 {
+	dx := startX - endX
+	dy := startY - endY
+	return math.Sqrt(float64(dx*dx) + float64(dy*dy))
+}