From 3abd4fa7833ccc68da916741678bb6241da2c09d Mon Sep 17 00:00:00 2001
From: Dreaded_X <tim.huizinga@gmail.com>
Date: Fri, 17 Dec 2021 20:23:52 +0100
Subject: [PATCH] 2021 - Day 17

---
 2021/17/go.mod  |   9 +++
 2021/17/go.sum  |   2 +
 2021/17/main.go | 143 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 154 insertions(+)
 create mode 100644 2021/17/go.mod
 create mode 100644 2021/17/go.sum
 create mode 100644 2021/17/main.go

diff --git a/2021/17/go.mod b/2021/17/go.mod
new file mode 100644
index 0000000..103619c
--- /dev/null
+++ b/2021/17/go.mod
@@ -0,0 +1,9 @@
+module AoC/2021/17
+
+require AoC/2021/common v0.0.0
+
+require github.com/joho/godotenv v1.4.0 // indirect
+
+replace AoC/2021/common v0.0.0 => ../common
+
+go 1.17
diff --git a/2021/17/go.sum b/2021/17/go.sum
new file mode 100644
index 0000000..8c9f290
--- /dev/null
+++ b/2021/17/go.sum
@@ -0,0 +1,2 @@
+github.com/joho/godotenv v1.4.0 h1:3l4+N6zfMWnkbPEXKng2o2/MR5mSwTrBih4ZEkkz1lg=
+github.com/joho/godotenv v1.4.0/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
diff --git a/2021/17/main.go b/2021/17/main.go
new file mode 100644
index 0000000..a7d2356
--- /dev/null
+++ b/2021/17/main.go
@@ -0,0 +1,143 @@
+package main
+
+import (
+	aoc "AoC/2021/common"
+	"bufio"
+	"fmt"
+	"regexp"
+	"strconv"
+)
+
+type vec struct {
+	x int
+	y int
+}
+
+type probe struct {
+	x vec
+	u vec
+}
+
+type target struct {
+	xmin int
+	xmax int
+	ymin int
+	ymax int
+}
+
+func (a *vec) add(b vec) {
+	a.x += b.x
+	a.y += b.y
+}
+
+func (v *vec) in(t target) bool {
+	return v.x >= t.xmin && v.x <= t.xmax && v.y >= t.ymin && v.y <= t.ymax
+}
+
+func (v *vec) past(t target) bool {
+	return v.x > t.xmax || v.y < t.ymin
+}
+
+func main() {
+	challenge := aoc.New(2021, 17)
+
+	challenge.Test(`target area: x=20..30, y=-10..-5`, []int{45, 112})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		input.Scan()
+		line := input.Text()
+
+		r := regexp.MustCompile("-?[0-9]+")
+
+		var coords [4]int
+		for i, c := range r.FindAllString(line, -1) {
+			coords[i], _ = strconv.Atoi(c)
+		}
+		t := target{coords[0], coords[1], coords[2], coords[3]}
+
+		max := 0
+		velocity := vec{0, 0}
+		for vx := -1000; vx < 1000; vx++ {
+			for vy := -1000; vy < 1000; vy++ {
+				p := probe{u: vec{vx, vy}}
+				height := 0
+				for step := 0; true; step++ {
+					if p.x.in(t) {
+						if height > max {
+							max = height
+							velocity = vec{vx, vy}
+						}
+
+						break
+					}
+
+					if p.x.past(t) {
+						break
+					}
+
+					if p.x.y > height {
+						height = p.x.y
+					}
+
+					p.x.add(p.u)
+
+					if p.u.x > 0 {
+						p.u.add(vec{-1, 0})
+					} else if p.u.x < 0 {
+						p.u.add(vec{1, 0})
+					}
+
+					p.u.add(vec{0, -1})
+				}
+
+			}
+		}
+
+		fmt.Printf("Max height %d is achieved using %v\n", max, velocity)
+
+		return max
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		input.Scan()
+		line := input.Text()
+
+		r := regexp.MustCompile("-?[0-9]+")
+
+		var coords [4]int
+		for i, c := range r.FindAllString(line, -1) {
+			coords[i], _ = strconv.Atoi(c)
+		}
+		t := target{coords[0], coords[1], coords[2], coords[3]}
+
+		counter := 0
+		for vx := -1000; vx < 1000; vx++ {
+			for vy := -1000; vy < 1000; vy++ {
+				p := probe{u: vec{vx, vy}}
+				for step := 0; true; step++ {
+					if p.x.in(t) {
+						counter++
+						break
+					}
+
+					if p.x.past(t) {
+						break
+					}
+
+					p.x.add(p.u)
+
+					if p.u.x > 0 {
+						p.u.add(vec{-1, 0})
+					} else if p.u.x < 0 {
+						p.u.add(vec{1, 0})
+					}
+
+					p.u.add(vec{0, -1})
+				}
+
+			}
+		}
+
+		return counter
+	})
+}