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solutions/day11/day11.go

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+package day11
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type Operation int
+
+const (
+	Times Operation = iota
+	Plus
+	Square
+)
+
+type Monkey struct {
+	items        []int
+	operation    Operation
+	operation_by int
+	divisible_by int
+	if_true      int
+	if_false     int
+}
+
+func printMonkeys(monkeys []*Monkey) {
+	for monkey_no, monkey := range monkeys {
+		if monkey != nil {
+			fmt.Printf("Monkey #%d: ", monkey_no)
+			var items []int = (*monkey).items
+			for idx, item := range items {
+				fmt.Printf("%d", item)
+				if idx != len(items)-1 {
+					fmt.Printf(", ")
+				}
+			}
+			fmt.Println()
+		}
+	}
+}
+
+func lcm(items []int) int {
+	worstCase := 1
+	smallest := items[0]
+	for _, val := range items {
+		worstCase *= val
+		if val < smallest {
+			smallest = val
+		}
+	}
+
+	retval := worstCase
+	for candidate := worstCase; candidate > 2; candidate -= smallest {
+		works := true
+		for _, val := range items {
+			works = works && (candidate%val == 0)
+		}
+		if works {
+			retval = candidate
+		}
+	}
+
+	return retval
+}
+
+func runRound(monkeys *[]*Monkey, counts *[]int, ceiling int) {
+	//three := big.NewInt(3)
+	for monkey_no, monkey := range *monkeys {
+		if monkey == nil {
+			break
+		}
+		//fmt.Printf("Monkey %d:\n", monkey_no)
+		items := (*monkey).items
+		(*monkey).items = []int{}
+		for _, item := range items {
+			(*counts)[monkey_no] += 1
+			//fmt.Printf("  Monkey inspects an item with a worry level of %d.\n", item)
+			var result int = item
+			switch monkey.operation {
+			case Times:
+				result = item * monkey.operation_by
+				//fmt.Printf("   Worry level is multiplied by %d to %d.\n", monkey.operation_by, result)
+			case Square:
+				result = item * item
+				//fmt.Printf("   Worry level is squared to %d.\n", result)
+			case Plus:
+				result = item + monkey.operation_by
+				//fmt.Printf("   Worry level is increased by %d to %d.\n", monkey.operation_by, result)
+			default:
+				//fmt.Printf("PANIC: Don't understand operation\n", monkey.operation_by)
+				return
+			}
+			result %= ceiling
+			//result = result.Div(result, three)
+			//fmt.Printf("   Monkey gets bored with item. Worry level is divided by 3 to %d.\n", result)
+			var targetMonkey int
+
+			if result%monkey.divisible_by == 0 {
+				//fmt.Printf("   Current worry level is divisible by %d.\n", monkey.divisible_by)
+				targetMonkey = monkey.if_true
+			} else {
+				//fmt.Printf("   Current worry level is not divisible by %d.\n", monkey.divisible_by)
+				targetMonkey = monkey.if_false
+			}
+			//fmt.Printf("   Item with worry level %d is thrown to monkey %d.\n", result, targetMonkey)
+			(*monkeys)[targetMonkey].items = append((*monkeys)[targetMonkey].items, result)
+		}
+	}
+}
+
+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 := []*Monkey{nil, nil, nil, nil, nil, nil, nil, nil}
+	inspectionCounts := []int{0, 0, 0, 0, 0, 0, 0, 0}
+	divisors := []int{}
+	var currentMonkey *Monkey = nil
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		if strings.HasPrefix(line, "Monkey ") {
+			number, err := strconv.Atoi(line[7 : len(line)-1])
+			if err != nil {
+				fmt.Println("Error parsing monkey number", line[7:len(line)-1])
+				return
+			}
+
+			newMonkey := Monkey{[]int{}, Times, 0, 0, 0, 0}
+			monkeys[number] = &newMonkey
+			currentMonkey = &newMonkey
+		} else if strings.HasPrefix(line, "  Starting items: ") {
+			list := line[18:]
+			splits := strings.Split(list, ", ")
+			if currentMonkey == nil {
+				fmt.Println("Item list with no monkey")
+				return
+			}
+			for _, split := range splits {
+				splitInt, err := strconv.Atoi(split)
+				if err != nil {
+					fmt.Println("Error parsing monkey's item", split)
+					return
+				}
+				(*currentMonkey).items = append((*&currentMonkey).items, splitInt)
+			}
+		} else if strings.HasPrefix(line, "  Operation: new = old * ") {
+			amtString := line[25:]
+			if amtString == "old" {
+				(*currentMonkey).operation = Square
+			} else {
+				amt, err := strconv.Atoi(amtString)
+				if err != nil {
+					fmt.Println("Error parsing operation number", amtString)
+					return
+				}
+				(*&currentMonkey).operation = Times
+				(*&currentMonkey).operation_by = amt
+			}
+		} else if strings.HasPrefix(line, "  Operation: new = old + ") {
+			amtString := line[25:]
+			amt, err := strconv.Atoi(amtString)
+			if err != nil {
+				fmt.Println("Error parsing plus operation number", amtString)
+				return
+			}
+			(*&currentMonkey).operation = Plus
+			(*&currentMonkey).operation_by = amt
+		} else if strings.HasPrefix(line, "  Test: divisible by ") {
+			amtString := line[21:]
+			amt, err := strconv.Atoi(amtString)
+			if err != nil {
+				fmt.Println("Error parsing divisible by number", amtString)
+				return
+			}
+			(*&currentMonkey).divisible_by = amt
+			divisors = append(divisors, amt)
+		} else if strings.HasPrefix(line, "    If true: throw to monkey ") {
+			amtString := line[29:]
+			amt, err := strconv.Atoi(amtString)
+			if err != nil {
+				fmt.Println("Error parsing if true number", amtString)
+				return
+			}
+			(*&currentMonkey).if_true = amt
+		} else if strings.HasPrefix(line, "    If false: throw to monkey ") {
+			amtString := line[30:]
+			amt, err := strconv.Atoi(amtString)
+			if err != nil {
+				fmt.Println("Error parsing if false number", amtString)
+				return
+			}
+			(*&currentMonkey).if_false = amt
+		} else if len(line) == 0 {
+		} else {
+			fmt.Printf("Invalid line: '%s'\n", line)
+			return
+		}
+	}
+
+	ceiling := lcm(divisors)
+
+	printMonkeys(monkeys)
+	for i := 0; i < 10000; i++ {
+		if i%100 == 0 {
+			fmt.Println("Running round", i)
+		}
+		runRound(&monkeys, &inspectionCounts, ceiling)
+		//printMonkeys(monkeys)
+	}
+	for monkey_no, count := range inspectionCounts {
+		fmt.Printf("Monkey %d inspected items %d times\n", monkey_no, count)
+	}
+
+	file.Close()
+}