Day 20

2016/day20/main.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/bogosj/advent-of-code/fileinput"
+	"github.com/bogosj/advent-of-code/intmath"
+)
+
+type ipRange struct {
+	start, end int
+}
+
+func (i ipRange) overlaps(oi ipRange) bool {
+	return oi.start >= i.start && oi.start <= i.end+1
+}
+
+func (i ipRange) mergeWith(oi ipRange) ipRange {
+	return ipRange{start: i.start, end: intmath.Max(i.end, oi.end)}
+}
+
+func input() (ret []ipRange) {
+	lines := fileinput.ReadLines("input.txt")
+	for _, line := range lines {
+		f := strings.FieldsFunc(line, func(r rune) bool { return r == '-' })
+		ret = append(ret, ipRange{start: intmath.Atoi(f[0]), end: intmath.Atoi(f[1])})
+	}
+	return
+}
+
+func mergedRanges(in []ipRange) []ipRange {
+	var mergedRanges []ipRange
+	sort.Slice(in, func(i, j int) bool { return in[i].start < in[j].start })
+	for len(in) > 0 {
+		if len(in) == 1 {
+			mergedRanges = append(mergedRanges, in[0])
+			in = nil
+			continue
+		}
+		if in[0].overlaps(in[1]) {
+			nr := in[0].mergeWith(in[1])
+			in = append([]ipRange{nr}, in[2:]...)
+		} else {
+			mergedRanges = append(mergedRanges, in[0])
+			in = in[1:]
+		}
+	}
+	return mergedRanges
+}
+
+func part1() {
+	mr := mergedRanges(input())
+	fmt.Println("The lowest valued IP is:", mr[0].end+1)
+}
+
+func part2() {
+	mr := mergedRanges(input())
+	ips := 0
+	for i := 0; i < len(mr)-1; i++ {
+		ips += mr[i+1].start - mr[i].end - 1
+	}
+	r := mr[len(mr)-1]
+	if r.end < 4294967295 {
+		ips += 4294967295 - r.end - 1
+	}
+	fmt.Println(ips, "IPs are allowed by the blocklist.")
+}
+
+func main() {
+	start := time.Now()
+	part1()
+	fmt.Println("Part 1 done in:", time.Since(start))
+	start = time.Now()
+	part2()
+	fmt.Println("Part 2 done in:", time.Since(start))
+}