Day 21 go

Author: pvainio

2021/go/d21/main.go

@@ -0,0 +1,96 @@
+package main
+
+import (
+	"fmt"
+)
+
+type Player struct {
+	pos, score int
+}
+
+type State struct {
+	totalRolls, prevRoll, prevRoll2 int
+	players                         [2]Player
+}
+
+// Advent of Code (AOC) 2021 Day 21 Dira Dice
+func main() {
+	state := State{players: [2]Player{{pos: 8}, {pos: 6}}}
+	for !state.gameOver(1000) {
+		state = state.rollPracticeDice()
+	}
+
+	losingScore := state.players[0].score
+	if state.players[1].score < losingScore {
+		losingScore = state.players[1].score
+	}
+	fmt.Printf("part 1: %v\n", losingScore*state.totalRolls)
+
+	state = State{players: [2]Player{{pos: 8}, {pos: 6}}}
+	cache := map[State][2]int64{}
+	res := playRecursiveUniverses(state, cache)
+
+	max := res[0]
+	if res[1] > max {
+		max = res[1]
+	}
+
+	fmt.Printf("part 2: %v\n", max)
+}
+
+// return number of wins as array player1, player2
+func playRecursiveUniverses(state State, cache map[State][2]int64) [2]int64 {
+	res, ok := cache[state]
+	if !ok {
+		for i := 1; i <= 3; i++ { // play Dira Dice all faces 1,2,3 and count winners together
+			lr := playRound(i, state, cache)
+			res[0] += lr[0]
+			res[1] += lr[1]
+		}
+		cache[state] = res
+	}
+	return res
+}
+
+// return number of wins as array player1, player2
+func playRound(currentRoll int, state State, cache map[State][2]int64) [2]int64 {
+	state = state.roll(currentRoll)
+
+	if state.gameOver(21) { // We have winner, return it as array 0,1 or 1,0
+		res := [2]int64{0, 0}
+		currentPlayer := (state.totalRolls / 3) % 2
+		res[currentPlayer] = 1
+		return res
+	}
+	return playRecursiveUniverses(state, cache)
+}
+
+func (state State) gameOver(score int) bool {
+	return state.players[0].score >= score || state.players[1].score >= score
+}
+
+func (state State) rollPracticeDice() State {
+	currentRoll := (state.totalRolls)%100 + 1
+	return state.roll(currentRoll)
+}
+
+func (state State) roll(currentRoll int) State {
+	playerRollNumber := state.totalRolls % 3 // number of rolls for current player
+	currentPlayer := (state.totalRolls / 3) % 2
+	state.totalRolls += 1
+
+	if playerRollNumber == 2 {
+		// third roll for the player, move it
+		totalRollSum := currentRoll + state.prevRoll + state.prevRoll2 // rolls sum
+		moved := state.players[currentPlayer].move(totalRollSum)
+		state.players[currentPlayer] = moved
+	}
+	state.prevRoll, state.prevRoll2 = currentRoll, state.prevRoll
+	return state
+}
+
+func (p Player) move(move int) Player {
+	pos := (p.pos+move-1)%10 + 1
+	score := pos + p.score
+	return Player{pos, score}
+}