Day11

2024/gareth/day11/day11.go

@@ -0,0 +1,89 @@
+package day11
+
+import (
+	"strconv"
+	"strings"
+)
+
+func Part1(input string) int {
+	stones := ParseInput(input)
+	return len(blinkTimes(stones, 25))
+}
+
+func Part2(input string) int {
+	stones := ParseInput(input)
+	return getNumStones(stones, 75)
+}
+
+func ParseInput(input string) []int {
+	strStones := strings.Split(strings.TrimSpace(input), " ")
+	stones := make([]int, 0, len(strStones))
+	for _, s := range strStones {
+		num, _ := strconv.Atoi(s)
+		stones = append(stones, num)
+	}
+	return stones
+}
+
+// Part 1 initial thought of recursion
+func blinkTimes(stones []int, times int) []int {
+	if times <= 0 {
+		return stones
+	}
+	result := blink(stones)
+	return blinkTimes(result, times-1)
+}
+
+func blink(stones []int) []int {
+	result := make([]int, 0)
+	for _, stone := range stones {
+		strStone := strconv.Itoa(stone)
+		if stone == 0 {
+			result = append(result, 1)
+		} else if len(strStone)%2 == 0 {
+			mid := len(strStone) / 2
+			firstHalf, _ := strconv.Atoi(strStone[:mid])
+			secondHalf, _ := strconv.Atoi(strStone[mid:])
+			result = append(result, firstHalf, secondHalf)
+		} else {
+			result = append(result, stone*2024)
+		}
+	}
+	return result
+}
+
+// Part 2 with maps since blinkTimes(75) would set my computer on fire
+func getNumStones(s []int, times int) int {
+	stoneMap := make(map[int]int)
+	for _, stone := range s {
+		stoneMap[stone] = stoneMap[stone] + 1
+	}
+
+	for i := 0; i < times; i++ {
+		stoneMap2 := make(map[int]int)
+		for stone, count := range stoneMap {
+			stones := make([]int, 0)
+			strStone := strconv.Itoa(stone)
+			if stone == 0 {
+				stones = append(stones, 1)
+			} else if len(strStone)%2 == 0 {
+				mid := len(strStone) / 2
+				firstHalf, _ := strconv.Atoi(strStone[:mid])
+				secondHalf, _ := strconv.Atoi(strStone[mid:])
+				stones = append(stones, firstHalf, secondHalf)
+			} else {
+				stones = append(stones, stone*2024)
+			}
+			for _, newStone := range stones {
+				stoneMap2[newStone] = stoneMap2[newStone] + count
+			}
+		}
+		stoneMap = stoneMap2
+	}
+
+	result := 0
+	for _, count := range stoneMap {
+		result += count
+	}
+	return result
+}