From 81bfde00b4c0b16b0ec8cac9bfe8e943841e0d5e Mon Sep 17 00:00:00 2001
From: Dreaded_X <tim.huizinga@gmail.com>
Date: Thu, 16 Dec 2021 18:42:41 +0100
Subject: [PATCH] 2021 - Day 16

---
 2021/16/go.mod  |   9 +++
 2021/16/go.sum  |   2 +
 2021/16/main.go | 182 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 193 insertions(+)
 create mode 100644 2021/16/go.mod
 create mode 100644 2021/16/go.sum
 create mode 100644 2021/16/main.go

diff --git a/2021/16/go.mod b/2021/16/go.mod
new file mode 100644
index 0000000..5c17eb2
--- /dev/null
+++ b/2021/16/go.mod
@@ -0,0 +1,9 @@
+module AoC/2021/16
+
+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/2021/16/go.sum b/2021/16/go.sum
new file mode 100644
index 0000000..8c9f290
--- /dev/null
+++ b/2021/16/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/2021/16/main.go b/2021/16/main.go
new file mode 100644
index 0000000..1f6953f
--- /dev/null
+++ b/2021/16/main.go
@@ -0,0 +1,182 @@
+package main
+
+import (
+	"AoC/2021/common"
+	"bufio"
+	"encoding/hex"
+)
+
+// Also implements a special operator -1, this operator will sum the versions of all (sub)packages
+func parsePackage(data []int, offset int, operator int, numberOfPackets int, lengthOfPackets int) (int, int) {
+	total := 0
+	// If we are going to multiply we need to start with 1
+	if operator == 1 {
+		total = 1
+	}
+
+	start := offset
+	for packetNumber := 0; (packetNumber < numberOfPackets || lengthOfPackets > offset - start); packetNumber++ {
+		version := 0
+		for i := 0; i < 3; i++ {
+			version <<= 1
+			version += data[offset + i]
+		}
+		offset += 3
+
+		typeID := 0
+		for i := 0; i < 3; i++ {
+			typeID <<= 1
+			typeID += data[offset + i]
+		}
+		offset += 3
+
+		value := 0
+		if typeID == 4 {
+			done := false
+			for !done {
+				done = data[offset + 0] == 0
+				offset++
+				for i := 0; i < 4; i++ {
+					value <<= 1
+					value += data[offset + i]
+				}
+				offset += 4
+			}
+
+			if operator == -1 {
+				value = version
+			}
+		} else {
+			lengthTypeID := data[offset + 0]
+			offset++
+
+			lop := 0
+			nop := 0
+			if lengthTypeID == 0 {
+				for i := 0; i < 15; i++ {
+					lop <<= 1
+					lop += data[offset + i]
+				}
+				offset += 15
+			} else if lengthTypeID == 1 {
+				for i := 0; i < 11; i++ {
+					nop <<= 1
+					nop += data[offset + i]
+				}
+				offset += 11
+			} else {
+				panic("Unknown lengthTypeID")
+			}
+
+			if operator == -1 {
+				typeID = -1
+			}
+
+			offset, value = parsePackage(data, offset, typeID, nop, lop)
+
+			if operator == -1 {
+				value += version
+			}
+		}
+
+		switch operator {
+		case -1, 0:
+			total += value
+		case 1:
+			total *= value
+		case 2:
+			if value < total || packetNumber == 0 {
+				total = value
+			}
+		case 3:
+			if value > total || packetNumber == 0 {
+				total = value
+			}
+		case 5:
+			if packetNumber == 0 {
+				total = value
+			} else if packetNumber == 1 {
+				if total > value {
+					total = 1
+				} else {
+					total = 0
+				}
+			} else {
+				panic("To many sub packets for 'greater than' operator")
+			}
+		case 6:
+			if packetNumber == 0 {
+				total = value
+			} else if packetNumber == 1 {
+				if total < value {
+					total = 1
+				} else {
+					total = 0
+				}
+			} else {
+				panic("To many sub packets for 'less than' operator")
+			}
+		case 7:
+			if packetNumber == 0 {
+				total = value
+			} else if packetNumber == 1 {
+				if total == value {
+					total = 1
+				} else {
+					total = 0
+				}
+			} else {
+				panic("To many sub packets for 'equal to' operator")
+			}
+		}
+	}
+
+	return offset, total
+}
+
+func parseInput(input *bufio.Scanner) []int {
+	input.Scan()
+	in, _ := hex.DecodeString(input.Text())
+
+	var data []int
+	for _, b := range in {
+		for i := 7; i >= 0; i-- {
+			data = append(data, int((b >> i) & 1))
+		}
+	}
+
+	return data
+}
+
+func main() {
+	challenge := aoc.New(2021, 16)
+
+	challenge.Test(`D2FE28`, []int{6, -2})
+	challenge.Test(`8A004A801A8002F478`, []int{16, -2})
+	challenge.Test(`620080001611562C8802118E34`, []int{12, -2})
+	challenge.Test(`C0015000016115A2E0802F182340`, []int{23, -2})
+	challenge.Test(`A0016C880162017C3686B18A3D4780`, []int{31, -2})
+
+	challenge.Test(`C200B40A82`, []int{-2, 3})
+	challenge.Test(`04005AC33890`, []int{-2, 54})
+	challenge.Test(`880086C3E88112`, []int{-2, 7})
+	challenge.Test(`CE00C43D881120`, []int{-2, 9})
+	challenge.Test(`D8005AC2A8F0`, []int{-2, 1})
+	challenge.Test(`F600BC2D8F`, []int{-2, 0})
+	challenge.Test(`9C005AC2F8F0`, []int{-2, 0})
+	challenge.Test(`9C0141080250320F1802104A08`, []int{-2, 1})
+
+	challenge.Solution(1, func (input *bufio.Scanner) int {
+		data := parseInput(input)
+		_, sum := parsePackage(data, 0, -1, 1, 0)
+
+		return sum
+	})
+
+	challenge.Solution(2, func (input *bufio.Scanner) int {
+		data := parseInput(input)
+		_, sum := parsePackage(data, 0, 0, 1, 0)
+
+		return sum
+	})
+}