From 3b5bae794815c2e825b7a5efd4662d0a364af551 Mon Sep 17 00:00:00 2001
From: Brian Buller <brian@bullercodeworks.com>
Date: Wed, 23 Dec 2020 09:29:58 -0600
Subject: [PATCH] 2020 Day 23 Complete!

---
 2020/day23/input     |   1 +
 2020/day23/main.go   | 228 +++++++++++++++++++++++++++++++++++++++++++
 2020/day23/testinput |   1 +
 3 files changed, 230 insertions(+)
 create mode 100644 2020/day23/input
 create mode 100644 2020/day23/main.go
 create mode 100644 2020/day23/testinput

diff --git a/2020/day23/input b/2020/day23/input
new file mode 100644
index 0000000..c4108a7
--- /dev/null
+++ b/2020/day23/input
@@ -0,0 +1 @@
+614752839
diff --git a/2020/day23/main.go b/2020/day23/main.go
new file mode 100644
index 0000000..eeceb78
--- /dev/null
+++ b/2020/day23/main.go
@@ -0,0 +1,228 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+var highest int
+var lowest int
+var AllCups map[int]*Cup
+
+func init() {
+	highest = h.MIN_INT
+	lowest = h.MAX_INT
+	AllCups = make(map[int]*Cup)
+}
+
+func main() {
+	fmt.Println("# Day 22")
+	inp := h.StdinToString()
+
+	solve(inp, h.Atoi(h.OptArgNumber(1, "2")))
+}
+
+var move int
+var first *Cup
+
+func solve(inp string, part int) {
+	moves := 100
+	if part == 1 {
+		BuildCircle(inp, -1)
+	} else {
+		BuildCircle(inp, 1000000)
+		moves = 10000000
+	}
+	current := first
+	for i := 0; i < moves; i++ {
+		current = DoMove(current)
+	}
+	ans := FindLabel(1, first).next
+	fmt.Println("## Part", part, ":\nAnswer:")
+	if part == 1 {
+		for ans.label != 1 {
+			fmt.Print(ans.label)
+			ans = ans.next
+		}
+	} else {
+		fmt.Print(ans.label * ans.next.label)
+	}
+	fmt.Println()
+}
+
+func BuildCircle(inp string, cups int) *Cup {
+	var wrk *Cup
+	for k := range inp {
+		next := &Cup{label: int(inp[k] - '0')}
+		next.next = next
+		next.prev = next
+		if first == nil {
+			first = next
+			first.next = next
+			first.prev = next
+		} else {
+			wrk.SetNext(next)
+		}
+		if next.label > highest {
+			highest = next.label
+		}
+		if next.label < lowest {
+			lowest = next.label
+		}
+		AllCups[next.label] = next
+		wrk = next
+	}
+	total := Count(first)
+	last := GetLast(first)
+	nextLabel := highest + 1
+	for cups > 0 && total < cups {
+		next := &Cup{label: nextLabel}
+		nextLabel++
+		next.next = next
+		next.prev = next
+		last.SetNext(next)
+		last = next
+		if next.label > highest {
+			highest = next.label
+		}
+		if next.label < lowest {
+			lowest = next.label
+		}
+		AllCups[next.label] = next
+		total++
+	}
+	return first
+}
+
+func DoMove(curr *Cup) *Cup {
+	move++
+	hold := curr.RemoveNext(3)
+	target := curr.label - 1
+	if target < lowest {
+		target = highest
+	}
+	// Check the removed cups
+	for FindLabel(target, hold) != nil {
+		target = target - 1
+		if target < lowest {
+			target = highest
+		}
+	}
+	//dest := FindLabel(target, curr)
+	dest := AllCups[target]
+	dest.SetNext(hold)
+	return curr.next
+}
+
+func FindLabel(num int, first *Cup) *Cup {
+	if first.label == num {
+		return first
+	}
+	c := first.next
+	for c != first {
+		if c.label == num {
+			return c
+		}
+		c = c.next
+	}
+	return nil
+}
+
+func StringifyCircle(first *Cup, current *Cup) string {
+	c := first
+	stringify := func(c *Cup) string {
+		if c == nil {
+			return "ERR"
+		}
+		if c == current {
+			return fmt.Sprintf("(%d)", c.label)
+		} else {
+			return fmt.Sprintf(" %d ", c.label)
+		}
+	}
+	ret := stringify(c)
+	c = c.next
+	for c != first {
+		ret = ret + stringify(c)
+		if c == nil {
+			ret = ret + " ERR "
+			break
+		}
+		if c.next == c {
+			break
+		}
+		c = c.next
+	}
+	return ret
+}
+
+func GetLast(cups *Cup) *Cup {
+	if cups.next == cups || cups.next == nil {
+		return cups
+	}
+	c := cups.next
+	for c.next != cups {
+		if c.next == nil {
+			break
+		}
+		c = c.next
+	}
+	return c
+}
+
+func Count(cups *Cup) int {
+	start := cups
+	wrk := start.next
+	ret := 1
+	for wrk != start {
+		wrk = wrk.next
+		ret++
+	}
+	return ret
+}
+
+var current *Cup
+
+type Cup struct {
+	label int
+	next  *Cup
+	prev  *Cup
+}
+
+func (c *Cup) SetNext(next *Cup) {
+	if c.next == c {
+		c.prev = next
+		c.next = next
+		next.next = c
+		next.prev = c
+		return
+	}
+	hold := c.next
+	// c.p c c.n
+	// c.p c next... c.n
+	c.next = next
+	if hold != nil {
+		hold.prev = GetLast(next)
+		GetLast(next).next = hold
+	}
+	next.prev = c
+}
+
+// RemoveNext removes the next cnt cups, returning a circle of the removed cups
+func (c *Cup) RemoveNext(cnt int) *Cup {
+	if cnt == 0 {
+		return nil
+	}
+	hold := c.next
+	dest := hold
+	for cnt > 0 {
+		dest = dest.next
+		cnt--
+	}
+	c.next = dest
+	dest.prev.next = hold
+	hold.prev = dest.prev
+	dest.prev = c
+	return hold
+}
diff --git a/2020/day23/testinput b/2020/day23/testinput
new file mode 100644
index 0000000..ab40847
--- /dev/null
+++ b/2020/day23/testinput
@@ -0,0 +1 @@
+389125467