From c8cc6d34ae625abe8a4c1c4c9cc8aa65791ab45e Mon Sep 17 00:00:00 2001
From: Anna Wiggins <annabunches@gmail.com>
Date: Fri, 11 Dec 2020 03:32:15 +0000
Subject: [PATCH] Add day 6 solution.

---
 2020/day04.go            | 20 ++-----------
 2020/day06.go            | 61 ++++++++++++++++++++++++++++++++++++++++
 2020/lib/util/strings.go | 21 ++++++++++++++
 3 files changed, 84 insertions(+), 18 deletions(-)
 create mode 100644 2020/day06.go
 create mode 100644 2020/lib/util/strings.go

diff --git a/2020/day04.go b/2020/day04.go
index dc234f2..41fa5b3 100644
--- a/2020/day04.go
+++ b/2020/day04.go
@@ -9,25 +9,9 @@ import (
 	"strings"
 
 	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/util"
 )
 
-func splitPassports(input []string) []string {
-	converted := []string{}
-
-	current := ""
-	for _, line := range input {
-		if line == "" {
-			converted = append(converted, current)
-			current = ""
-			continue
-		}
-
-		current += " " + line
-	}
-
-	return converted
-}
-
 func countValidPassports(input []string, step string) int {
 	total := 0
 	for _, line := range input {
@@ -147,7 +131,7 @@ func makeInt(input string) int {
 func main() {
 	step := os.Args[1]
 	values := fileutils.InputParserStrings(os.Args[2])
-	values = splitPassports(values)
+	values = util.SplitOnBlankLine(values)
 
 	fmt.Println("Valid Passports:", countValidPassports(values, step))
 }
diff --git a/2020/day06.go b/2020/day06.go
new file mode 100644
index 0000000..00a6e2c
--- /dev/null
+++ b/2020/day06.go
@@ -0,0 +1,61 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/util"
+)
+
+func countAnswerUnion(input string) int {
+	charMap := make(map[rune]bool)
+
+	for _, char := range input {
+		if char == ' ' {
+			continue
+		}
+
+		if _, ok := charMap[char]; !ok {
+			charMap[char] = true
+		}
+	}
+	return len(charMap)
+}
+
+func countAnswerIntersection(input string) int {
+	charMap := make(map[rune]int)
+	answers := strings.Split(strings.Trim(input, " "), " ")
+
+	for _, answer := range answers {
+		for _, char := range answer {
+			charMap[char]++
+		}
+	}
+
+	total := 0
+	for _, count := range charMap {
+		if count == len(answers) {
+			total++
+		}
+	}
+	return total
+}
+
+func main() {
+	step := os.Args[1]
+	values := fileutils.InputParserStrings(os.Args[2])
+	groups := util.SplitOnBlankLine(values)
+
+	total := 0
+	for _, line := range groups {
+		if step == "1" {
+			total += countAnswerUnion(line)
+		}
+		if step == "2" {
+			total += countAnswerIntersection(line)
+		}
+	}
+	fmt.Println("Total:", total)
+}
diff --git a/2020/lib/util/strings.go b/2020/lib/util/strings.go
new file mode 100644
index 0000000..a2f35ae
--- /dev/null
+++ b/2020/lib/util/strings.go
@@ -0,0 +1,21 @@
+package util
+
+// Takes a slice of strings as from reading each line in a file.
+// Concatenates strings, creating new ones when blank lines are encountered
+// NB: adds a single space to the beginning of each concatenated line.
+func SplitOnBlankLine(input []string) []string {
+	converted := []string{}
+
+	current := ""
+	for _, line := range input {
+		if line == "" {
+			converted = append(converted, current)
+			current = ""
+			continue
+		}
+
+		current += " " + line
+	}
+
+	return converted
+}