Day 19 Complete

2016/day19/main.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"fmt"
+
+	"../../"
+)
+
+// pt1 input: 3014387
+func main() {
+	partOne := aoc.ArgIsSet("-1")
+	num := 3014387
+	if aoc.ArgIsSet("-test") {
+		num = 5 // Example
+	}
+	firstElf := CreateElf(1)
+	t := CreateElf(2)
+	firstElf.setLeft(t)
+	t.setRight(firstElf)
+	fmt.Println("Generating Elves...")
+	for i := 3; i <= num; i++ {
+		nextElf := CreateElf(i)
+		nextElf.setRight(t)
+		t.setLeft(nextElf)
+		t = nextElf
+	}
+	t.setLeft(firstElf)
+	firstElf.setRight(t)
+
+	fmt.Println(num, "Elves Generated.")
+	fmt.Println("Initiating Greed Injection...")
+
+	t = firstElf
+	if !partOne {
+		t = GetElfAcrossCircle(t, num)
+	}
+	for t.getLeft() != t {
+		if partOne {
+			// Remove the elf to the left
+			t = t.getLeft()
+			t = t.remove()
+			num--
+		} else {
+			// Remove the current elf, the next elf to be removed is the one to the left
+			// (remove() returns a pointer to the elf to it's left)
+			t = t.remove()
+			if num%2 == 1 {
+				// Unless we have an odd number of elves, then we skip this one
+				t = t.getLeft()
+			}
+			num--
+		}
+	}
+	fmt.Println("The lucky elf is elf #", t.getId())
+}
+
+func GetElfAcrossCircle(e *Elf, num int) *Elf {
+	retElf := e
+	for i := 0; i < num/2; i++ {
+		retElf = retElf.getLeft()
+	}
+	return retElf
+}
+
+type Elf struct {
+	id      int
+	out     bool
+	toRight *Elf
+	toLeft  *Elf
+}
+
+// To keep the game running smoothly, an elf is required to
+// let the gamemaster know who the elf to their left is when they
+// are eliminated
+func (e *Elf) remove() *Elf {
+	e.getLeft().setRight(e.getRight())
+	e.getRight().setLeft(e.getLeft())
+	return e.getLeft()
+}
+
+func (e *Elf) getId() int {
+	return e.id
+}
+
+func (e *Elf) getRight() *Elf {
+	return e.toRight
+}
+
+func (e *Elf) setRight(r *Elf) {
+	e.toRight = r
+}
+
+func (e *Elf) getLeft() *Elf {
+	return e.toLeft
+}
+
+func (e *Elf) setLeft(l *Elf) {
+	e.toLeft = l
+}
+
+func CreateElf(id int) *Elf {
+	r := new(Elf)
+	r.id = id
+	return r
+}

2016/day19/problem

@@ -0,0 +1,106 @@
+Advent of Code
+
+--- Day 19: An Elephant Named Joseph ---
+
+   The Elves contact you over a highly secure emergency channel. Back at the
+   North Pole, the Elves are busy misunderstanding White Elephant parties.
+
+   Each Elf brings a present. They all sit in a circle, numbered starting
+   with position 1. Then, starting with the first Elf, they take turns
+   stealing all the presents from the Elf to their left. An Elf with no
+   presents is removed from the circle and does not take turns.
+
+   For example, with five Elves (numbered 1 to 5):
+
+   1
+ 5   2
+  4 3
+
+     • Elf 1 takes Elf 2's present.
+     • Elf 2 has no presents and is skipped.
+     • Elf 3 takes Elf 4's present.
+     • Elf 4 has no presents and is also skipped.
+     • Elf 5 takes Elf 1's two presents.
+     • Neither Elf 1 nor Elf 2 have any presents, so both are skipped.
+     • Elf 3 takes Elf 5's three presents.
+
+   So, with five Elves, the Elf that sits starting in position 3 gets all the
+   presents.
+
+   With the number of Elves given in your puzzle input, which Elf gets all
+   the presents?
+
+   Your puzzle input was 3014387.
+
+   Your puzzle answer was __________.
+
+--- Part Two ---
+
+   Realizing the folly of their present-exchange rules, the Elves agree to
+   instead steal presents from the Elf directly across the circle. If two
+   Elves are across the circle, the one on the left (from the perspective of
+   the stealer) is stolen from. The other rules remain unchanged: Elves with
+   no presents are removed from the circle entirely, and the other elves move
+   in slightly to keep the circle evenly spaced.
+
+   For example, with five Elves (again numbered 1 to 5):
+
+     • The Elves sit in a circle; Elf 1 goes first:
+
+   1
+ 5   2
+  4 3
+
+     • Elves 3 and 4 are across the circle; Elf 3's present is stolen, being
+       the one to the left. Elf 3 leaves the circle, and the rest of the
+       Elves move in:
+
+   1           1
+ 5   2  -->  5   2
+  4 -          4
+
+     • Elf 2 steals from the Elf directly across the circle, Elf 5:
+
+   1         1
+ -   2  -->     2
+   4         4
+
+     • Next is Elf 4 who, choosing between Elves 1 and 2, steals from Elf 1:
+
+  -          2
+     2  -->
+  4          4
+
+     • Finally, Elf 2 steals from Elf 4:
+
+  2
+     -->  2
+  -
+
+   So, with five Elves, the Elf that sits starting in position 2 gets all the
+   presents.
+
+   With the number of Elves given in your puzzle input, which Elf now gets
+   all the presents?
+
+   Your puzzle input was 3014387.
+
+   Your puzzle answer was __________.
+
+References
+
+   Visible links
+   . http://adventofcode.com/
+   . http://adventofcode.com/2016/about
+   . http://adventofcode.com/2016/support
+   . http://adventofcode.com/2016/events
+   . http://adventofcode.com/2016/settings
+   . http://adventofcode.com/2016/auth/logout
+   . http://adventofcode.com/2016
+   . http://adventofcode.com/2016
+   . http://adventofcode.com/2016/leaderboard
+   . http://adventofcode.com/2016/stats
+   . http://adventofcode.com/2016/sponsors
+   . http://adventofcode.com/2016/sponsors
+   . https://en.wikipedia.org/wiki/White_elephant_gift_exchange
+   . http://adventofcode.com/2016

helpers.go

@@ -7,8 +7,28 @@ import (
 	"log"
 	"os"
 	"strconv"
+	"strings"
 )
 
+func ArgIsSet(a string) bool {
+	for i := range os.Args {
+		if os.Args[i] == a || strings.HasPrefix(os.Args[i], a+"=") {
+			return true
+		}
+	}
+	return false
+}
+
+func GetArgValue(a string) string {
+	for i := range os.Args {
+		if strings.HasPrefix(os.Args[i], a+"=") {
+			return strings.TrimPrefix(os.Args[i], a+"=")
+		}
+	}
+	return ""
+
+}
+
 func StdinToStringSlice() []string {
 	var input []string
 	scanner := bufio.NewScanner(os.Stdin)