Day 20 Complete

2016/day20/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"sort"
+	"strings"
+
+	"../../"
+)
+
+func main() {
+	part1 := aoc.ArgIsSet("-1")
+	justSort := aoc.ArgIsSet("-sort")
+	input := aoc.StdinToStringSlice()
+	var blacklists []Blacklist
+	for i := range input {
+		pts := strings.Split(input[i], "-")
+		st := aoc.Atoi(pts[0])
+		end := aoc.Atoi(pts[1])
+		blacklists = append(blacklists, *CreateBlacklist(st, end))
+	}
+	sort.Sort(ByStart(blacklists))
+
+	// Just output the sorted blacklists
+	if justSort {
+		for i := range blacklists {
+			fmt.Print(blacklists[i].start, "-", blacklists[i].end, "\n")
+		}
+		return
+	}
+
+	// Find the lowest non-blacklisted IP
+	if part1 {
+		fmt.Println(findLowest(blacklists))
+		return
+	}
+
+	// Count how many IPs are allowed
+	var numIps, blIdx, ip int
+	highestIp := int(math.Pow(2, 32))
+	for ip <= highestIp {
+		if blIdx >= len(blacklists) {
+			break
+		}
+		if ip >= blacklists[blIdx].start {
+			if ip <= blacklists[blIdx].end {
+				ip = blacklists[blIdx].end + 1
+				continue
+			}
+			blIdx++
+		} else {
+			numIps++
+			ip++
+		}
+	}
+
+	fmt.Println(numIps)
+}
+
+func findLowest(blacklists []Blacklist) int {
+	var lowestIp int
+	for i := range blacklists {
+		if blacklists[i].hasIp(lowestIp) {
+			lowestIp = blacklists[i].end + 1
+		}
+	}
+	return lowestIp
+}
+
+type Blacklist struct {
+	start, end int
+}
+
+func CreateBlacklist(st, end int) *Blacklist {
+	return &Blacklist{st, end}
+}
+
+func (b *Blacklist) hasIp(inp int) bool {
+	return inp >= b.start && inp <= b.end
+}
+
+type ByStart []Blacklist
+
+func (b ByStart) Len() int           { return len(b) }
+func (b ByStart) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }
+func (b ByStart) Less(i, j int) bool { return b[i].start < b[j].start }