day 8

08/main.go

@@ -0,0 +1,207 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+func main() {
+	start := time.Now()
+	partOne()
+	duration := time.Since(start)
+	partTwo()
+	duration2 := time.Since(start)
+	fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
+}
+
+func makeScanner(test bool) *bufio.Scanner {
+	var f *os.File
+	if test {
+		f, _ = os.Open("inputs/testinput")
+	} else {
+		f, _ = os.Open("inputs/input")
+	}
+	reader := bufio.NewReader(f)
+	return bufio.NewScanner(reader)
+}
+
+type display struct {
+	inputs  []string
+	outputs []string
+	// mappings from input wires to display pieces
+	top         string
+	topleft     string
+	topright    string
+	center      string
+	bottomleft  string
+	bottomright string
+	bottom      string
+}
+
+func parseLine(line string) display {
+	display := display{
+		inputs:  make([]string, 0),
+		outputs: make([]string, 0),
+	}
+	acc := []byte{}
+	outputs := false
+	for i := 0; i < len(line); i++ {
+		switch line[i] {
+		case 'a', 'b', 'c', 'd', 'e', 'f', 'g':
+			acc = append(acc, line[i])
+		case ' ':
+			if !outputs {
+				display.inputs = append(display.inputs, string(acc))
+				acc = []byte{}
+			} else {
+				display.outputs = append(display.outputs, string(acc))
+				acc = []byte{}
+			}
+		case '|':
+			i++
+			acc = []byte{}
+			outputs = true
+		}
+	}
+	// and catch the last one
+	display.outputs = append(display.outputs, string(acc))
+	return display
+}
+
+func removeAll(s, remove string) string {
+	for _, v := range remove {
+		s = strings.ReplaceAll(s, string(v), "")
+	}
+	return s
+}
+
+func timesAppears(s string, list []string) (r int) {
+	for _, v := range list {
+		if strings.Contains(v, s) {
+			r++
+		}
+	}
+	return
+}
+
+func partOne() {
+	scanner := makeScanner(false)
+
+	displays := []display{}
+	for scanner.Scan() {
+		displays = append(displays, parseLine(scanner.Text()))
+	}
+	hit := 0
+	for _, display := range displays {
+		for _, v := range display.outputs {
+			if len(v) == 7 || len(v) == 4 || len(v) == 3 || len(v) == 2 { // 8, 4, 7, 1
+				hit++
+			}
+		}
+	}
+	fmt.Println(hit)
+}
+
+func solve(display *display) {
+	mapping := map[int]string{}
+	for _, v := range display.inputs {
+		if len(v) == 2 {
+			mapping[1] = v
+		}
+		if len(v) == 3 {
+			mapping[7] = v
+		}
+		if len(v) == 4 {
+			mapping[4] = v
+		}
+		if len(v) == 7 {
+			mapping[8] = v
+		}
+	}
+	for _, v := range []string{"a", "b", "c", "d", "e", "f", "g"} {
+		if timesAppears(v, display.inputs) == 9 {
+			display.bottomright = v
+		}
+		if timesAppears(v, display.inputs) == 4 {
+			display.bottomleft = v
+		}
+	}
+
+	display.top = removeAll(mapping[7], mapping[1])
+	display.bottom = removeAll(mapping[8], mapping[4]+mapping[7]+display.bottomleft)
+
+	// find 0
+	for _, v := range display.inputs {
+		if len(v) == 6 {
+			remainder := removeAll(v, display.top+display.bottomleft+display.bottom+mapping[1])
+			if len(remainder) == 1 { // this is "0", so we found top-left and center
+				display.topleft = remainder
+				display.center = removeAll(mapping[8], v)
+			}
+		}
+	}
+
+	display.topright = removeAll(mapping[8], display.top+display.topleft+display.center+display.bottomleft+display.bottomright+display.bottom)
+}
+
+func valueFromSolved(d display, unknown string) string {
+	if len(unknown) == 2 {
+		return "1"
+	}
+	if len(unknown) == 3 {
+		return "7"
+	}
+	if len(unknown) == 4 {
+		return "4"
+	}
+	if len(unknown) == 5 {
+		if strings.Contains(unknown, d.topright) && strings.Contains(unknown, d.bottomright) {
+			return "3"
+		}
+		if strings.Contains(unknown, d.topright) && strings.Contains(unknown, d.bottomleft) {
+			return "2"
+		}
+		if strings.Contains(unknown, d.topleft) && strings.Contains(unknown, d.bottomright) {
+			return "5"
+		}
+	}
+	if len(unknown) == 6 {
+		if !strings.Contains(unknown, d.center) {
+			return "0"
+		}
+		if !strings.Contains(unknown, d.bottomleft) {
+			return "9"
+		}
+		if !strings.Contains(unknown, d.topright) {
+			return "6"
+		}
+	}
+	if len(unknown) == 7 {
+		return "8"
+	}
+	panic("uhoh")
+}
+
+func partTwo() {
+	scanner := makeScanner(false)
+
+	displays := []display{}
+	for scanner.Scan() {
+		displays = append(displays, parseLine(scanner.Text()))
+	}
+	total := 0
+	for _, v := range displays {
+		solve(&v)
+		sub := ""
+		for _, integer := range v.outputs {
+			sub += valueFromSolved(v, integer)
+		}
+		i, _ := strconv.Atoi(sub)
+		total += i
+	}
+	fmt.Println(total)
+}