advent2022/solutions/day21/day21.go

package day21

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

const (
	OpAdd int = iota
	OpMul
	OpSub
	OpDiv
	OpTarget
)

func opString(v int) string {
	switch v {
	case OpAdd:
		return "+"
	case OpMul:
		return "*"
	case OpSub:
		return "-"
	case OpDiv:
		return "/"
	case OpTarget:
		return "=="
	default:
		return "???????"
	}
}

type MonkeyState struct {
	valueSet  bool
	value     int
	operation int
	left      string
	right     string
}

func step(monkeys map[string]MonkeyState) bool {
	changedSomething := false

	for monkey, state := range monkeys {
		if !state.valueSet && monkeys[state.left].valueSet && monkeys[state.right].valueSet {
			switch state.operation {
			case OpAdd:
				state.value = monkeys[state.left].value + monkeys[state.right].value
			case OpSub:
				state.value = monkeys[state.left].value - monkeys[state.right].value
			case OpMul:
				state.value = monkeys[state.left].value * monkeys[state.right].value
			case OpDiv:
				state.value = monkeys[state.left].value / monkeys[state.right].value
			}
			state.valueSet = true
			monkeys[monkey] = state
			changedSomething = true
		}
	}

	return changedSomething
}

func contains(ls []string, x string) bool {
	for _, tester := range ls {
		if tester == x {
			return true
		}
	}
	return false
}

func Run(filename string) {
	file, err := os.Open(filename)
	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}

	scanner := bufio.NewScanner(file)
	scanner.Split(bufio.ScanLines)
	monkeys := map[string]MonkeyState{}

	for scanner.Scan() {
		line := scanner.Text()

		monkey := line[0:4]
		data := line[6:]
		value, err := strconv.Atoi(data)
		if err == nil {
			monkeys[monkey] = MonkeyState{true, value, 0, "", ""}
		} else {
			left := data[0:4]
			right := data[7:]
			switch data[5] {
			case '+':
				monkeys[monkey] = MonkeyState{false, 0, OpAdd, left, right}
			case '-':
				monkeys[monkey] = MonkeyState{false, 0, OpSub, left, right}
			case '*':
				monkeys[monkey] = MonkeyState{false, 0, OpMul, left, right}
			case '/':
				monkeys[monkey] = MonkeyState{false, 0, OpDiv, left, right}
			default:
				fmt.Println("Bad operation", string(data[5]))
				return
			}
		}
	}
	file.Close()

	for !monkeys["root"].valueSet {
		step(monkeys)
	}
	fmt.Println("Root monkey value, part 1:", monkeys["root"].value)

	humn := monkeys["humn"]
	humn.valueSet = false
	humn.operation = OpTarget
	monkeys["humn"] = humn
	unwoundMonkeys := []string{"humn"}
	updatedSomething := true
	for updatedSomething {
		updatedSomething = false
		for monkey, state := range monkeys {
			if contains(unwoundMonkeys, state.left) || contains(unwoundMonkeys, state.right) {
				if state.valueSet {
					state.valueSet = false
					monkeys[monkey] = state
					unwoundMonkeys = append(unwoundMonkeys, monkey)
					updatedSomething = true
				}
			}
		}
	}

	fmt.Println("monkeys now", monkeys)
	var targetValue int
	var nextNode string

	if monkeys[monkeys["root"].left].valueSet {
		targetValue = monkeys[monkeys["root"].left].value
		nextNode = monkeys["root"].right
		fmt.Println("Root's right is the unknown one", nextNode)
	} else {
		targetValue = monkeys[monkeys["root"].right].value
		nextNode = monkeys["root"].left
		fmt.Println("Root's left is the unknown one", nextNode)
	}

	for !monkeys["humn"].valueSet {
		nextState := monkeys[nextNode]

		if nextState.valueSet {
			fmt.Println("PANIC: Grounded in a node with the value set")
			return
		} else if nextState.operation == OpTarget {
			nextState.value = targetValue
			nextState.valueSet = true
			monkeys[nextNode] = nextState
		} else if monkeys[nextState.left].valueSet {
			nextState.value = targetValue
			nextState.valueSet = true
			monkeys[nextNode] = nextState
			switch nextState.operation {
			case OpAdd:
				// T = V + X
				// T - V = X
				targetValue = targetValue - monkeys[nextState.left].value
			case OpMul:
				// T = V * X
				// T / V = X
				targetValue = targetValue / monkeys[nextState.left].value
			case OpSub:
				// T = V - X
				// T + X = V
				// X = V - T
				targetValue = monkeys[nextState.left].value - targetValue
			case OpDiv:
				// T = V / X
				// TX = V
				// X = V / T
				targetValue = monkeys[nextState.left].value / targetValue
			default:
				fmt.Println("PANIC: Bad operation in back compute")
			}
			nextNode = nextState.right
		} else if monkeys[nextState.right].valueSet {
			nextState.value = targetValue
			nextState.valueSet = true
			monkeys[nextNode] = nextState
			switch nextState.operation {
			case OpAdd:
				// T = X + V
				// T - V = X
				targetValue = targetValue - monkeys[nextState.right].value
			case OpMul:
				// T = X * V
				targetValue = targetValue / monkeys[nextState.right].value
			case OpSub:
				// T = X - V
				// T + V = X
				targetValue = targetValue + monkeys[nextState.right].value
			case OpDiv:
				// T = X / V
				// TV = X
				targetValue = targetValue * monkeys[nextState.right].value
			default:
				fmt.Println("PANIC: Bad operation in back compute")
			}
			nextNode = nextState.left
		} else {
			fmt.Println("PANIC: Trouble with a double split in search")
			return
		}
	}
	fmt.Println("Actually, my value should be", monkeys["humn"].value)
}