day21; a little bit hacky, but working

day21/day.go

@@ -0,0 +1,114 @@
+package day21
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"strings"
+	"tools"
+)
+
+var revIndex = map[int]int{
+	0: 1,
+	1: 1,
+	2: 6,
+	3: 2,
+	4: 7,
+	5: 3,
+	6: 8,
+	7: 4,
+}
+
+func scramble(s string, instr []string, reverse bool) string {
+	sb := []byte(s)
+	for _, inst := range instr {
+		parts := strings.Split(inst, " ")
+		if parts[0] == "swap" && parts[1] == "position" {
+			x, _ := strconv.Atoi(parts[2])
+			y, _ := strconv.Atoi(parts[5])
+			sb[x], sb[y] = sb[y], sb[x]
+		} else if parts[0] == "swap" && parts[1] == "letter" {
+			x := bytes.Index(sb, []byte(parts[2]))
+			y := bytes.Index(sb, []byte(parts[5]))
+			sb[x], sb[y] = sb[y], sb[x]
+		} else if parts[0] == "rotate" && parts[1] == "left" {
+			x, _ := strconv.Atoi(parts[2])
+			if reverse {
+				sb = append(sb[len(sb)-(x%len(sb)):], sb[:len(sb)-(x%len(sb))]...)
+			} else {
+				sb = append(sb[x%len(sb):], sb[:x%len(sb)]...)
+			}
+		} else if parts[0] == "rotate" && parts[1] == "right" {
+			x, _ := strconv.Atoi(parts[2])
+			if reverse {
+				sb = append(sb[x%len(sb):], sb[:x%len(sb)]...)
+			} else {
+				sb = append(sb[len(sb)-(x%len(sb)):], sb[:len(sb)-(x%len(sb))]...)
+			}
+		} else if parts[0] == "rotate" && parts[1] == "based" {
+			var x int
+			if reverse {
+				x = bytes.Index(sb, []byte(parts[6]))
+				x = revIndex[x]
+				sb = append(sb[x%len(sb):], sb[:x%len(sb)]...)
+			} else {
+				x = bytes.Index(sb, []byte(parts[6]))
+				if x >= 4 {
+					x++
+				}
+				x++
+				sb = append(sb[len(sb)-(x%len(sb)):], sb[:len(sb)-(x%len(sb))]...)
+			}
+		} else if parts[0] == "reverse" && parts[1] == "positions" {
+			x, _ := strconv.Atoi(parts[2])
+			y, _ := strconv.Atoi(parts[4])
+			var ns []byte
+			for i := 0; i < x; i++ {
+				ns = append(ns, sb[i])
+			}
+			for i := y; i >= x; i-- {
+				ns = append(ns, sb[i])
+			}
+			sb = append(ns, sb[y+1:]...)
+		} else if parts[0] == "move" && parts[1] == "position" {
+			x, _ := strconv.Atoi(parts[2])
+			y, _ := strconv.Atoi(parts[5])
+			if reverse {
+				c := sb[y]
+				sb = append(sb[:y], sb[y+1:]...)
+				sb = append(sb[:x+1], sb[x:]...)
+				sb[x] = c
+			} else {
+				c := sb[x]
+				sb = append(sb[:x], sb[x+1:]...)
+				sb = append(sb[:y+1], sb[y:]...)
+				sb[y] = c
+			}
+		} else {
+			fmt.Println("ERROR: unknown instruction:", inst)
+		}
+	}
+
+	return string(sb)
+}
+
+func Part1(puzzle tools.AoCPuzzle) interface{} {
+	inp := puzzle.GetInputArray()
+	startString := inp[0]
+	password := scramble(startString, inp[1:], false)
+
+	return password
+}
+
+func Part2(puzzle tools.AoCPuzzle) interface{} {
+	inp := puzzle.GetInputArray()
+	var rinp []string
+	for x := len(inp) - 1; x > 0; x-- {
+		rinp = append(rinp, inp[x])
+	}
+	startString := "fbgdceah"
+	//startString := "gfdhebac"
+	password := scramble(startString, rinp, true)
+
+	return password
+}

inputs/21

@@ -0,0 +1,101 @@
+abcdefgh
+reverse positions 1 through 6
+rotate based on position of letter a
+swap position 4 with position 1
+reverse positions 1 through 5
+move position 5 to position 7
+swap position 4 with position 0
+swap position 4 with position 6
+rotate based on position of letter a
+swap position 0 with position 2
+move position 5 to position 2
+move position 7 to position 1
+swap letter d with letter c
+swap position 5 with position 3
+reverse positions 3 through 7
+rotate based on position of letter d
+swap position 7 with position 5
+rotate based on position of letter f
+swap position 4 with position 1
+swap position 3 with position 6
+reverse positions 4 through 7
+rotate based on position of letter c
+move position 0 to position 5
+swap position 7 with position 4
+rotate based on position of letter f
+reverse positions 1 through 3
+move position 5 to position 3
+rotate based on position of letter g
+reverse positions 2 through 5
+rotate right 0 steps
+rotate left 0 steps
+swap letter f with letter b
+rotate based on position of letter h
+move position 1 to position 3
+reverse positions 3 through 6
+rotate based on position of letter h
+swap position 4 with position 3
+swap letter b with letter h
+swap letter a with letter h
+reverse positions 1 through 6
+swap position 3 with position 6
+swap letter e with letter d
+swap letter e with letter h
+swap position 1 with position 5
+rotate based on position of letter a
+reverse positions 4 through 5
+swap position 0 with position 4
+reverse positions 0 through 3
+move position 7 to position 2
+swap letter e with letter c
+swap position 3 with position 4
+rotate left 3 steps
+rotate left 7 steps
+rotate based on position of letter e
+reverse positions 5 through 6
+move position 1 to position 5
+move position 1 to position 2
+rotate left 1 step
+move position 7 to position 6
+rotate left 0 steps
+reverse positions 5 through 6
+reverse positions 3 through 7
+swap letter d with letter e
+rotate right 3 steps
+swap position 2 with position 1
+swap position 5 with position 7
+swap letter h with letter d
+swap letter c with letter d
+rotate based on position of letter d
+swap letter d with letter g
+reverse positions 0 through 1
+rotate right 0 steps
+swap position 2 with position 3
+rotate left 4 steps
+rotate left 5 steps
+move position 7 to position 0
+rotate right 1 step
+swap letter g with letter f
+rotate based on position of letter a
+rotate based on position of letter b
+swap letter g with letter e
+rotate right 4 steps
+rotate based on position of letter h
+reverse positions 3 through 5
+swap letter h with letter e
+swap letter g with letter a
+rotate based on position of letter c
+reverse positions 0 through 4
+rotate based on position of letter e
+reverse positions 4 through 7
+rotate left 4 steps
+swap position 0 with position 6
+reverse positions 1 through 6
+rotate left 2 steps
+swap position 5 with position 3
+swap letter b with letter d
+swap letter b with letter d
+rotate based on position of letter d
+rotate based on position of letter c
+rotate based on position of letter h
+move position 4 to position 7

inputs/21_test

@@ -0,0 +1,9 @@
+abcde
+swap position 4 with position 0
+swap letter d with letter b
+reverse positions 0 through 4
+rotate left 1 step
+move position 1 to position 4
+move position 3 to position 0
+rotate based on position of letter b
+rotate based on position of letter d

main.go

@@ -20,6 +20,7 @@ import (
 	"aoc2016/day18"
 	"aoc2016/day19"
 	"aoc2016/day20"
+	"aoc2016/day21"
 	"aoc2016/day23"
 	"aoc2016/day24"
 	"flag"
@@ -59,7 +60,7 @@ func initDayFunctions() {
 		18: {1: day18.Part1, 2: day18.Part2},
 		19: {1: day19.Part1, 2: day19.Part2},
 		20: {1: day20.Part1, 2: day20.Part2},
-		//		21: {1: day21.Part1, 2: day21.Part2},
+		21: {1: day21.Part1, 2: day21.Part2},
 		//		22: {1: day22.Part1, 2: day22.Part2},
 		23: {1: day23.Part1, 2: day23.Part2},
 		24: {1: day24.Part1, 2: day24.Part2},