Day 21 Complete

Added String Permutation helper to helpers file

2016/day21/main.go

@@ -0,0 +1,110 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"../../"
+)
+
+func main() {
+	pw := "fbgdceah" // Part 2 Puzzle input
+	input := aoc.StdinToStringSlice()
+	if aoc.ArgIsSet("-1") {
+		pw = "abcdefgh" // Part 1 Puzzle input
+		pw = scramblePassword(pw, input)
+		fmt.Println(scramblePassword(pw, input))
+		return
+	}
+	fmt.Println(unscramblePassword(pw, input))
+}
+
+func unscramblePassword(pw string, inst []string) string {
+	// Brute force it.
+	// Just get all permutations of the runes and return the one
+	// for which the instructions return the input
+	tst := aoc.StringPermutations(pw)
+	for i := range tst {
+		if scramblePassword(tst[i], inst) == pw {
+			return tst[i]
+		}
+	}
+	return ""
+}
+
+func scramblePassword(pw string, inst []string) string {
+	for i := range inst {
+		pts := strings.Fields(inst[i])
+		switch pts[0] + " " + pts[1] {
+		case "swap position":
+			pw = swapPos(pw, aoc.Atoi(pts[2]), aoc.Atoi(pts[5]))
+		case "swap letter":
+			pw = swapLetter(pw, pts[2], pts[5])
+		case "reverse positions":
+			pw = reverse(pw, aoc.Atoi(pts[2]), aoc.Atoi(pts[4]))
+		case "rotate left":
+			pw = rotate(pw, aoc.Atoi(pts[2])*-1)
+		case "rotate right":
+			pw = rotate(pw, aoc.Atoi(pts[2]))
+		case "rotate based":
+			rotIdx := strings.Index(pw, pts[6])
+			if rotIdx >= 4 {
+				rotIdx++
+			}
+			rotIdx++
+			pw = rotate(pw, rotIdx)
+		case "move position":
+			pw = move(pw, aoc.Atoi(pts[2]), aoc.Atoi(pts[5]))
+		}
+	}
+	return pw
+}
+
+func swapPos(pw string, x, y int) string {
+	r := []rune(pw)
+	r[x], r[y] = r[y], r[x]
+	return string(r)
+}
+
+func swapLetter(pw string, x, y string) string {
+	xPos := strings.Index(pw, x)
+	yPos := strings.Index(pw, y)
+	return swapPos(pw, xPos, yPos)
+}
+
+func rotate(pw string, steps int) string {
+	r := []rune(pw)
+	var x rune
+	for steps < 0 {
+		// Left rotate (shift & push)
+		x, r = r[0], r[1:]
+		r = append(r, x)
+		steps++
+	}
+	for steps > 0 {
+		// Right rotate (pop & unshift)
+		x, r = r[len(r)-1], r[:len(r)-1]
+		r = append([]rune{x}, r...)
+		steps--
+	}
+	return string(r)
+}
+
+func reverse(pw string, beg, end int) string {
+	revStr := pw[beg : end+1]
+	runes := []rune(revStr)
+	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
+		runes[i], runes[j] = runes[j], runes[i]
+	}
+	return pw[:beg] + string(runes) + pw[end+1:]
+}
+
+func move(pw string, x, y int) string {
+	r := []rune(pw)
+	// Cut element at x
+	mov := r[x]
+	r = append(r[:x], r[x+1:]...)
+	// Insert at y
+	r = append(r[:y], append([]rune{mov}, r[y:]...)...)
+	return string(r)
+}