From df30e9abc09f8f61645a96dfb7cbd5a54a1ad012 Mon Sep 17 00:00:00 2001
From: David Ashby <delta.mu.alpha@gmail.com>
Date: Sat, 26 Dec 2020 13:09:37 -0500
Subject: [PATCH] add day 23

---
 23/main.go | 137 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 137 insertions(+)
 create mode 100644 23/main.go

diff --git a/23/main.go b/23/main.go
new file mode 100644
index 0000000..9a82c4e
--- /dev/null
+++ b/23/main.go
@@ -0,0 +1,137 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+func cupInList(cup int, cups []int) bool {
+	for _, c := range cups {
+		if c == cup {
+			return true
+		}
+	}
+	return false
+}
+
+func generateFullCupset(cups []int, totalCups int) []int {
+	for i := len(cups); i < totalCups; i = i + 1 {
+		cups = append(cups, i)
+	}
+	return cups
+}
+
+func findTargetCupIndex(cup int, cups []int) int {
+	for i, c := range cups {
+		if c == cup {
+			return i
+		}
+	}
+	return 0 // uh-oh
+}
+
+func step(cups []int) []int {
+	cupCount := len(cups)
+	currentCup := cups[0]
+	removedCups := cups[1:4]
+	newList := make([]int, 0, cupCount)
+	newList = append([]int{cups[0]}, cups[4:]...)
+	var targetCup int
+	if currentCup == 1 {
+		targetCup = cupCount
+	} else {
+		targetCup = currentCup - 1
+	}
+	for cupInList(targetCup, removedCups) {
+		targetCup = targetCup - 1
+		if targetCup == 0 {
+			targetCup = cupCount
+		}
+	}
+	tc := findTargetCupIndex(targetCup, newList)
+	result := make([]int, 0, cupCount)
+	result = append(result, newList[1:tc+1]...)
+	result = append(result, removedCups...)
+	result = append(result, newList[tc+1:]...)
+	result = append(result, newList[0])
+	return result
+}
+
+func runabout(cups []int) string {
+	oneIndex := findTargetCupIndex(1, cups)
+	result := ""
+	for i := oneIndex + 1; i < len(cups); i = i + 1 {
+		result = result + strconv.Itoa(cups[i])
+	}
+	for i := 0; i < len(cups[:oneIndex]); i = i + 1 {
+		result = result + strconv.Itoa(cups[i])
+	}
+	return result
+}
+
+func nextTwo(cups []int) (int, int) {
+	oneIndex := findTargetCupIndex(1, cups)
+	if oneIndex+1 > len(cups) {
+		return cups[0], cups[1]
+	}
+	if oneIndex+2 > len(cups) {
+		return cups[len(cups)], cups[0]
+	}
+	return cups[oneIndex+1], cups[oneIndex+2]
+}
+
+func partOne() {
+	f, _ := os.Open("testinput")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	cups := []int{}
+
+	scanner.Scan()
+	for _, s := range strings.Split(scanner.Text(), "") {
+		i, _ := strconv.Atoi(s)
+		cups = append(cups, i)
+	}
+
+	for i := 0; i < 100; i = i + 1 {
+		cups = step(cups)
+	}
+
+	fmt.Println(runabout(cups))
+
+}
+
+func partTwo() {
+	f, _ := os.Open("testinput")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	cups := []int{}
+
+	scanner.Scan()
+	for _, s := range strings.Split(scanner.Text(), "") {
+		i, _ := strconv.Atoi(s)
+		cups = append(cups, i)
+	}
+
+	allCups := generateFullCupset(cups, 10000000)
+	for i := 0; i < 10000000; i = i + 1 {
+		allCups = step(allCups)
+		fmt.Println(i)
+	}
+
+	fmt.Println(nextTwo(allCups))
+}