From f5daf337a9c25f3354aa2cf8e7b072ae39291270 Mon Sep 17 00:00:00 2001
From: Maximilian Friedersdorff <max@friedersdorff.com>
Date: Mon, 11 Mar 2019 19:17:04 +0000
Subject: [PATCH] Solution for problem 102: Triangle containment

---
 102_triangle_containment/main.go | 94 ++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 102_triangle_containment/main.go

diff --git a/102_triangle_containment/main.go b/102_triangle_containment/main.go
new file mode 100644
index 0000000..7a2d4b6
--- /dev/null
+++ b/102_triangle_containment/main.go
@@ -0,0 +1,94 @@
+package main
+
+import (
+	"encoding/csv"
+	"errors"
+	"fmt"
+	"git.friedersdorff.com/max/vector.go"
+	"os"
+	"strconv"
+)
+
+// sameSide returns true if p1 and p2 are on the same side of the line ab, false
+// otherwise
+func sameSide(p1, p2, a, b vector.Vec) bool {
+	cp1 := b.Sub(a).Cross(p1.Sub(a))
+	cp2 := b.Sub(a).Cross(p2.Sub(a))
+
+	return cp1.Dot(cp2) >= 0
+}
+
+// inTriangle returns true if point p is in triangle abc, false otherwise
+func inTriangle(p, a, b, c vector.Vec) bool {
+	return sameSide(p, a, b, c) && sameSide(p, b, a, c) && sameSide(p, c, a, b)
+}
+
+func getVec(record []string) ([]vector.Vec, error) {
+	if len(record)%2 != 0 {
+		return nil, errors.New(
+			fmt.Sprintf("Length of record is not divisible by 2: %s",
+				len(record)))
+	}
+	var vecs []vector.Vec
+
+	floats := make([]float64, len(record))
+	for i, v := range record {
+		num, err := strconv.ParseFloat(v, 64)
+
+		if err != nil {
+			return nil, errors.New(
+				fmt.Sprintf("Couldn't parse record to floats: %s",
+					record))
+		}
+
+		floats[i] = num
+	}
+
+	for i := 0; i < len(floats); i += 2 {
+		vecs = append(vecs, vector.Vec{floats[i], floats[i+1], 0.0})
+	}
+	return vecs, nil
+
+}
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Println("Expect input file as first argument.")
+		return
+	}
+
+	f, err := os.Open(os.Args[1])
+
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+
+	r := csv.NewReader(f)
+
+	nInTriangle := 0
+	for {
+		triangle, err := r.Read()
+		if err != nil {
+			break
+		}
+
+		points, err := getVec(triangle)
+		if err != nil {
+
+			break
+		}
+
+		if len(points) != 3 {
+			break
+		}
+
+		if inTriangle(vector.Vec{0, 0, 0},
+			points[0], points[1], points[2]) {
+			nInTriangle++
+		}
+	}
+
+	fmt.Println(nInTriangle)
+	return
+}
-- 
2.46.2