Day 23: Part 1

Signed-off-by: James Griffin <james@unsupervised.ca>

main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/thatguygriff/aoc2020/twentytwo"
+	"github.com/thatguygriff/aoc2020/twentythree"
 )
 
 func main() {
@@ -92,6 +92,9 @@ func main() {
 	// fmt.Println(twentyone.PartTwo())
 
 	// Day 22
-	fmt.Println(twentytwo.PartOne())
+	// fmt.Println(twentytwo.PartOne())
-	fmt.Println(twentytwo.PartTwo())
+	// fmt.Println(twentytwo.PartTwo())
+
+	// Day 23
+	fmt.Println(twentythree.PartOne())
 }

twentythree/day_twentythree.go

@@ -0,0 +1,104 @@
+package twentythree
+
+import (
+	"fmt"
+	"strconv"
+)
+
+type game struct {
+	cups       []int
+	currentCup int
+	highestCup int
+}
+
+func (g *game) load(input string) error {
+	for _, c := range input {
+		cupNumber, err := strconv.Atoi(string(c))
+		if err != nil {
+			return err
+		}
+		if cupNumber > g.highestCup {
+			g.highestCup = cupNumber
+		}
+		g.cups = append(g.cups, cupNumber)
+	}
+
+	if len(g.cups) > 0 {
+		g.currentCup = g.cups[0]
+	}
+
+	return nil
+}
+
+func (g *game) play(moves int) string {
+	for i := 0; i < moves; i++ {
+		// pickup cups
+		pickup := g.cups[1:4]
+		remaining := []int{g.cups[0]}
+		remaining = append(remaining, g.cups[4:]...)
+		g.cups = remaining
+
+		// find destination cup
+		destination := false
+		destinationIndex := -1
+		t := g.currentCup - 1
+		for !destination {
+			if t <= 0 {
+				t = g.highestCup
+			}
+
+			for i := 1; i < len(g.cups); i++ {
+				if g.cups[i] == t {
+					destinationIndex = i
+					break
+				}
+			}
+
+			if destinationIndex != -1 {
+				destination = true
+			}
+			t--
+		}
+
+		// place cups
+		newOrder := []int{}
+		for _, c := range remaining[:destinationIndex+1] {
+			newOrder = append(newOrder, c)
+		}
+		newOrder = append(newOrder, pickup...)
+		for _, c := range remaining[destinationIndex+1:] {
+			newOrder = append(newOrder, c)
+		}
+		g.cups = newOrder
+
+		// Update current cup
+		g.cups = g.cups[1:]
+		g.cups = append(g.cups, g.currentCup)
+		g.currentCup = g.cups[0]
+	}
+
+	return g.output()
+}
+
+func (g *game) output() string {
+	state := []int{}
+	for i, c := range g.cups {
+		if c == 1 {
+			state = append(state, g.cups[i+1:]...)
+			state = append(state, g.cups[:i]...)
+		}
+	}
+	output := ""
+	for _, n := range state {
+		output += fmt.Sprintf("%d", n)
+	}
+
+	return output
+}
+
+// PartOne What are the labels on the cups after cup 1
+func PartOne() string {
+	g := game{}
+	g.load("418976235")
+	return g.play(100)
+}

twentythree/day_twentythree_test.go

@@ -0,0 +1,60 @@
+package twentythree
+
+import "testing"
+
+func Test_load_input(t *testing.T) {
+	g := game{}
+	g.load("32415")
+
+	if len(g.cups) != 5 {
+		t.Logf("Expected 5 cups. Got %d", len(g.cups))
+		t.FailNow()
+	}
+
+	if g.highestCup != 5 {
+		t.Logf("Expected highest cup to be 5, found %d", g.highestCup)
+		t.FailNow()
+	}
+}
+
+func Test_10_moves(t *testing.T) {
+	g := game{}
+	g.load("389125467")
+
+	if len(g.cups) != 9 {
+		t.Logf("Expected 9 cups. Got %d", len(g.cups))
+		t.FailNow()
+	}
+
+	if g.highestCup != 9 {
+		t.Logf("Expected highest cup to be 9, found %d", g.highestCup)
+		t.FailNow()
+	}
+
+	tenMoves := g.play(10)
+	if tenMoves != "92658374" {
+		t.Logf("Expected \"92658374\" but found %q", tenMoves)
+		t.FailNow()
+	}
+}
+
+func Test_100_moves(t *testing.T) {
+	g := game{}
+	g.load("389125467")
+
+	if len(g.cups) != 9 {
+		t.Logf("Expected 9 cups. Got %d", len(g.cups))
+		t.FailNow()
+	}
+
+	if g.highestCup != 9 {
+		t.Logf("Expected highest cup to be 9, found %d", g.highestCup)
+		t.FailNow()
+	}
+
+	hundredMoves := g.play(100)
+	if hundredMoves != "67384529" {
+		t.Logf("Expected \"67384529\" but found %q", hundredMoves)
+		t.FailNow()
+	}
+}