Added solutions for 8th day : the seven segments code to guess

1 files changed, 143 insertions, 0 deletions

diff --git a/2021/08/second.go b/2021/08/second.go
new file mode 100644
index 0000000..e71c23b
--- /dev/null
+++ b/2021/08/second.go
@@ -0,0 +1,143 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+func sortStrings(strs []string) {
+	for i, v := range strs {
+		s := strings.Split(v, "")
+		sort.Strings(s)
+		strs[i] = strings.Join(s, "")
+	}
+}
+
+func deduceSix(one string, zns []string) string { // zns == zero, nine and six
+	for _, v := range zns {
+		for _, c := range one {
+			if !strings.Contains(v, string(c)) {
+				return v
+			}
+		}
+	}
+	log.Fatalf("deduce(%+v, %+v) failed!", one, zns)
+	return ""
+}
+
+func deduceTwoThreeFive(ttf []string, topRight, bottomRight byte) (two string, three string, five string) {
+	for _, s := range ttf {
+		if !strings.Contains(s, string(topRight)) {
+			five = s
+		} else if !strings.Contains(s, string(bottomRight)) {
+			two = s
+		} else {
+			three = s
+		}
+	}
+	return
+}
+
+func deduceRight(one, six string) (byte, byte) {
+	if strings.Contains(six, string(one[0])) {
+		return one[1], one[0]
+	} else {
+		return one[0], one[1]
+	}
+}
+
+func deduceBottomLeft(one, two, five string) byte {
+	for _, ch := range two {
+		s := string(ch)
+		if strings.Contains(one, s) || strings.Contains(five, s) {
+			continue
+		}
+		return s[0]
+	}
+	log.Fatalf("deduceBottomLeft(%+v, %+v, %+v) failed!", one, two, five)
+	return 0 // cannot happen
+}
+
+func deduceZeroNine(zsn []string, six string, bottomLeft byte) (zero string, nine string) {
+	for _, s := range zsn {
+		if s == six {
+			continue
+		}
+		if strings.Contains(s, string(bottomLeft)) {
+			zero = s
+		} else {
+			nine = s
+		}
+	}
+	return
+}
+
+func main() {
+	score := 0
+
+	s := bufio.NewScanner(os.Stdin)
+	for s.Scan() {
+		inputs := strings.Split(s.Text(), " | ")
+		hints := strings.Split(inputs[0], " ")
+		outputs := strings.Split(inputs[1], " ")
+		sort.Slice(hints, func(i, j int) bool {
+			return len(hints[i]) < len(hints[j])
+		})
+		sortStrings(hints)
+		sortStrings(outputs)
+
+		// some digits are straightforward :
+		one := hints[0]
+		seven := hints[1]
+		four := hints[2]
+		eight := hints[9]
+
+		// We can deduce number 6 by being in len 6 and missing a component from 1
+		six := deduceSix(one, hints[6:9])
+		// the right segments can be deduced from the one in 1 that is in the 6
+		topRight, bottomRight := deduceRight(one, six)
+		// We can deduce numbers two, three and five from the right segments
+		two, three, five := deduceTwoThreeFive(hints[3:6], topRight, bottomRight)
+		// We can deduce the bottom left segment from 1 2 and 5
+		bottomLeft := deduceBottomLeft(one, two, five)
+		// We can deduce numbers 0 and 9 from the bottom left segment and the fact we already know 6
+		zero, nine := deduceZeroNine(hints[6:9], six, bottomLeft)
+
+		key := make([]byte, 4)
+		for i, s := range outputs {
+			switch s {
+			case zero:
+				key[i] = '0'
+			case one:
+				key[i] = '1'
+			case two:
+				key[i] = '2'
+			case three:
+				key[i] = '3'
+			case four:
+				key[i] = '4'
+			case five:
+				key[i] = '5'
+			case six:
+				key[i] = '6'
+			case seven:
+				key[i] = '7'
+			case eight:
+				key[i] = '8'
+			case nine:
+				key[i] = '9'
+			default:
+				fmt.Println(zero, one, two, three, four, five, six, seven, eight, nine)
+				log.Fatalf("Did not find %+v", s)
+			}
+		}
+		v, _ := strconv.Atoi(string(key))
+		score += v
+	}
+	fmt.Println(score)
+}