2020-day15 so close :( 600/209. difficult to just understand the prompt. brute forced a dictionary for pt 2

2017-day10 weird fake hashing, xor and hexadecimals

2017/day10/main.go

@@ -0,0 +1,116 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/mathutil"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"), 256)
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	}
+}
+
+func part1(input string, listLength int) int {
+	lengths := parseInput(input)
+
+	nums := make([]int, listLength)
+	for i := range nums {
+		nums[i] = i
+	}
+	var position, skipSize int
+	for _, length := range lengths {
+		if length > 0 {
+			nums = reverse(nums, position, position+length-1)
+		}
+		position += skipSize + length
+		position %= len(nums)
+		skipSize++
+	}
+
+	return nums[0] * nums[1]
+}
+
+func part2(input string) string {
+	lengths := parseInputASCII(input)
+	nums := make([]int, 256)
+	for i := range nums {
+		nums[i] = i
+	}
+	var position, skipSize int
+
+	for round := 0; round < 64; round++ {
+		for _, length := range lengths {
+			if length > 0 {
+				nums = reverse(nums, position, position+length-1)
+			}
+			position += skipSize + length
+			position %= len(nums)
+			skipSize++
+		}
+	}
+
+	var denseHash []int
+	for i := 0; i < 16; i++ {
+		var xord int
+		for j := i * 16; j < (i+1)*16; j++ {
+			xord ^= nums[j]
+		}
+		denseHash = append(denseHash, xord)
+	}
+
+	var hexdHash string
+	for _, dense := range denseHash {
+		// use %x to get hexadecimal version & 02 ensures leading 0 if needed
+		hexdHash += fmt.Sprintf("%02x", dense)
+	}
+
+	return hexdHash
+}
+
+func reverse(nums []int, left, right int) []int {
+	right %= len(nums)
+	if right < left {
+		right += len(nums)
+	}
+
+	for left < right {
+		leftModded := left % len(nums)
+		rightModded := right % len(nums)
+		nums[leftModded], nums[rightModded] = nums[rightModded], nums[leftModded]
+		left++
+		right--
+	}
+
+	return nums
+}
+
+func parseInput(input string) (ans []int) {
+	nums := strings.Split(input, ",")
+	for _, num := range nums {
+		ans = append(ans, mathutil.StrToInt(num))
+	}
+	return ans
+}
+
+func parseInputASCII(input string) (ans []int) {
+	for _, char := range input {
+		ans = append(ans, int(char))
+	}
+	// add default lengths to end
+	ans = append(ans, 17, 31, 73, 47, 23)
+	return ans
+}

2017/day10/main_test.go

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func Test_part1(t *testing.T) {
+	tests := []struct {
+		name       string
+		input      string
+		listLength int
+		want       int
+	}{
+		{"example", "3,4,1,5", 5, 12},
+		{"actual", util.ReadFile("input.txt"), 256, 212},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input, tt.listLength); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_part2(t *testing.T) {
+	tests := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{"example", "1,2,3", "3efbe78a8d82f29979031a4aa0b16a9d"},
+		{"actual", util.ReadFile("input.txt"), "96de9657665675b51cd03f0b3528ba26"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part2(tt.input); got != tt.want {
+				t.Errorf("part2() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}