day22p2

day22p2/solution.go

@@ -0,0 +1,60 @@
+package day22p2
+
+import (
+	"io"
+	"strconv"
+
+	"aoc/utils"
+)
+
+func Solve(r io.Reader) any {
+	lines := utils.ReadLines(r)
+
+	seqToProfit := make(map[[4]int]int)
+	visited := make(map[[4]int]bool)
+	for _, line := range lines {
+		var seq [4]int
+		clear(visited)
+		initialSecretNum, _ := strconv.Atoi(line)
+		newSecretNum := initialSecretNum
+		for i := 0; i < 2000; i++ {
+			prevPrice := newSecretNum % 10
+			newSecretNum = evolveSecretNum(newSecretNum)
+			price := newSecretNum % 10
+			diff := price - prevPrice
+			seq[0], seq[1], seq[2], seq[3] = seq[1], seq[2], seq[3], diff
+			if i < 3 {
+				continue
+			}
+			if !visited[seq] {
+				seqToProfit[seq] += price
+				visited[seq] = true
+			}
+		}
+	}
+
+	maxProfit := 0
+	for _, profit := range seqToProfit {
+		if profit > maxProfit {
+			maxProfit = profit
+		}
+	}
+
+	return maxProfit
+}
+
+func evolveSecretNum(initialSecretNum int) int {
+	secretNum := initialSecretNum
+	secretNum = prune(mix(secretNum, secretNum*64))
+	secretNum = prune(mix(secretNum, secretNum/32))
+	secretNum = prune(mix(secretNum, secretNum*2048))
+	return secretNum
+}
+
+func mix(a, b int) int {
+	return a ^ b
+}
+
+func prune(a int) int { // modulo 16777216 (2^24)
+	return a & 0xFFFFFF
+}

day22p2/solution_test.go

@@ -0,0 +1,36 @@
+package day22p2
+
+import (
+	"strings"
+	"testing"
+
+	"aoc/utils"
+)
+
+var testInput = `1
+2
+3
+2024`
+
+func TestSolve(t *testing.T) {
+	tests := []struct {
+		input  string
+		answer int
+	}{
+		{testInput, 23},
+	}
+
+	if testing.Verbose() {
+		utils.Verbose = true
+	}
+
+	for _, test := range tests {
+		r := strings.NewReader(test.input)
+
+		result := Solve(r).(int)
+
+		if result != test.answer {
+			t.Errorf("Expected %d, got %d", test.answer, result)
+		}
+	}
+}