From 9f357a759101cb5b5288649dc4c9c6a840a0d98a Mon Sep 17 00:00:00 2001
From: Ben Charlton <ben@spod.cx>
Date: Wed, 20 Dec 2017 11:09:32 +0000
Subject: [PATCH] day 20

---
 20/20.go | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 20/20.go

diff --git a/20/20.go b/20/20.go
new file mode 100644
index 0000000..a2c8217
--- /dev/null
+++ b/20/20.go
@@ -0,0 +1,97 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type particle struct {
+	px int
+	py int
+	pz int
+	vx int
+	vy int
+	vz int
+	ax int
+	ay int
+	az int
+}
+
+// cat input | go run 20.go
+
+func main() {
+
+	var particles []particle
+
+	scanner := bufio.NewScanner(os.Stdin)
+
+	for scanner.Scan() {
+		t1 := strings.Split(scanner.Text(), ">")
+		p1 := strings.Split(t1[0], "<")
+		v1 := strings.Split(t1[1], "<")
+		a1 := strings.Split(t1[2], "<")
+
+		p := strings.Split(p1[1], ",")
+		v := strings.Split(v1[1], ",")
+		a := strings.Split(a1[1], ",")
+
+		p = append(p, v...)
+		p = append(p, a...)
+
+		var keep []int
+		for i := range p {
+			x, _ := strconv.Atoi(strings.Trim(p[i], " "))
+			keep = append(keep, x)
+		}
+
+		part := particle{keep[0], keep[1], keep[2], keep[3], keep[4], keep[5], keep[6], keep[7], keep[8]}
+		particles = append(particles, part)
+	}
+
+	for {
+
+		closest := 999999999999999999
+		closestParticle := -1
+
+		collide := make(map[string]int)
+
+		for i := range particles {
+			current := particles[i]
+			current.vx += current.ax
+			current.vy += current.ay
+			current.vz += current.az
+			current.px += current.vx
+			current.py += current.vy
+			current.pz += current.vz
+
+			test := fmt.Sprint(current.px, current.py, current.pz)
+			collide[test]++
+
+			dist := int(math.Abs(float64(current.px)) + math.Abs(float64(current.py)) + math.Abs(float64(current.pz)))
+			if dist < closest {
+				closest = dist
+				closestParticle = i
+			}
+			particles[i] = current
+		}
+
+		// Make new array of non-collision particles
+		var new []particle
+		for r := range particles {
+			current := particles[r]
+			test := fmt.Sprint(current.px, current.py, current.pz)
+			t, _ := collide[test]
+			if t < 2 {
+				new = append(new, particles[r])
+			}
+		}
+		particles = new
+
+		fmt.Println(closestParticle, len(particles))
+	}
+
+}