day20

day19/day.go

@@ -42,10 +42,9 @@ func Part2(puzzle tools.AoCPuzzle) interface{} {
 		elfs = append(elfs, i+1)
 	}
 
-	// Does one half not always eliminate the other half +/- 1? Not Quite!!!
-	// Does it eliminate half of the "upper" half? As in "every second one"? Also not Quite!
+	// Future optimization path?
 	// 0..4; 0 eliminates 2 (index + floor(half), 1 eliminates 4 (1 + half(len)), 3 eliminates 1 (index + floor(half))
-	// (1:?)2:1:2:1:...until len(2) (start with 1 for equal lens and 2 for unequal lens)
+	// eliminate (1:?)2:1:2:1:...until len(2) (start with 1 for equal lens and 2 for unequal lens)
 	for len(elfs) > 1 {
 		half := int(math.Floor(float64(len(elfs) / 2)))
 		elfs = append(elfs, elfs[0])

day20/day.go

@@ -0,0 +1,56 @@
+package day20
+
+import (
+	"sort"
+	"strconv"
+	"strings"
+	"tools"
+)
+
+func getBlacklistMap(inp []string) (map[int]int, []int) {
+	ips := make(map[int]int)
+	var lips []int
+	for _, l := range inp {
+		p := strings.Split(l, "-")
+		i1, _ := strconv.Atoi(p[0])
+		i2, _ := strconv.Atoi(p[1])
+		ips[i1] = i2
+		lips = append(lips, i1)
+	}
+	sort.Ints(lips)
+	return ips, lips
+}
+
+func Part1(puzzle tools.AoCPuzzle) interface{} {
+	ips, lips := getBlacklistMap(puzzle.GetInputArray())
+
+	index := 0
+	for _, lip := range lips {
+		if lip > index {
+			break
+		}
+		if index >= lip && index <= ips[lip] {
+			index = ips[lip] + 1
+		}
+	}
+
+	return index
+}
+
+func Part2(puzzle tools.AoCPuzzle) interface{} {
+	ips, lips := getBlacklistMap(puzzle.GetInputArray())
+
+	cips := make(map[int]int)
+	var minIp, maxIp = 0, 0
+	for _, lip := range lips {
+		if lip >= minIp && lip <= maxIp+1 {
+			maxIp = tools.Max(ips[lip], maxIp)
+		} else {
+			minIp = lip
+			maxIp = ips[lip]
+		}
+		cips[minIp] = maxIp
+	}
+
+	return len(cips) - 1
+}

inputs/20_test

@@ -0,0 +1,3 @@
+5-8
+0-2
+4-7

main.go

@@ -19,6 +19,7 @@ import (
 	"aoc2016/day17"
 	"aoc2016/day18"
 	"aoc2016/day19"
+	"aoc2016/day20"
 	"flag"
 	"fmt"
 	"os"
@@ -55,7 +56,7 @@ func initDayFunctions() {
 		17: {1: day17.Part1, 2: day17.Part2},
 		18: {1: day18.Part1, 2: day18.Part2},
 		19: {1: day19.Part1, 2: day19.Part2},
-		//		20: {1: day20.Part1, 2: day20.Part2},
+		20: {1: day20.Part1, 2: day20.Part2},
 		//		21: {1: day21.Part1, 2: day21.Part2},
 		//		22: {1: day22.Part1, 2: day22.Part2},
 		//		23: {1: day23.Part1, 2: day23.Part2},