From 15c41ba2279e8895dbf8e42a3518d59d33ed2419 Mon Sep 17 00:00:00 2001
From: alexchao26 <alexchaoo@gmail.com>
Date: Sat, 12 Dec 2020 21:23:40 -0500
Subject: [PATCH] 2018-day25: UGLY graph grouping solution...but 2018
 completed!

---
 2018/day25/main.go      | 97 +++++++++++++++++++++++++++++++++++++++++
 2018/day25/main_test.go | 64 +++++++++++++++++++++++++++
 2 files changed, 161 insertions(+)
 create mode 100644 2018/day25/main.go
 create mode 100644 2018/day25/main_test.go

diff --git a/2018/day25/main.go b/2018/day25/main.go
new file mode 100644
index 0000000..bcd113d
--- /dev/null
+++ b/2018/day25/main.go
@@ -0,0 +1,97 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(util.ReadFile("./input.txt"))
+		fmt.Println("Output:", ans)
+	} else {
+		panic("no part 2 :P")
+	}
+}
+
+func part1(input string) int {
+	allCoords := parseInput(input)
+
+	constellations := [][][4]int{}
+
+	for _, iterCoord := range allCoords {
+		// check which constellations this coordinate is in range of
+		indicesWithinRange := []int{}
+		for constIndex, constellation := range constellations {
+			for _, constCoord := range constellation {
+				if manhattanDistance(constCoord, iterCoord) <= 3 {
+					indicesWithinRange = append(indicesWithinRange, constIndex)
+					break
+				}
+			}
+		}
+
+		// if no existing constellations are within range, append a new one with
+		// just this current coordinate
+		if len(indicesWithinRange) == 0 {
+			constellations = append(constellations, [][4]int{iterCoord})
+		} else {
+			// otherwise merge all constellations together (into the first one)
+			// add the current node
+			// then remove any other constellations that were merged into #1
+			firstIndex := indicesWithinRange[0]
+			for i, indexToMerge := range indicesWithinRange {
+				if i != 0 {
+					current := constellations[indexToMerge]
+					constellations[firstIndex] = append(constellations[firstIndex], current...)
+				}
+			}
+			constellations[firstIndex] = append(constellations[firstIndex], iterCoord)
+
+			// remove all but the first constellation, in reverse order b/c
+			// using this method for removal affects the end of the slice, and
+			// in some cases that may be the element that we want to remove
+			for i := len(indicesWithinRange) - 1; i > 0; i-- {
+				constIndex := indicesWithinRange[i]
+				lastIndex := len(constellations) - 1
+				constellations[constIndex] = constellations[lastIndex]
+				constellations = constellations[:lastIndex]
+			}
+		}
+	}
+
+	return len(constellations)
+}
+
+func parseInput(input string) [][4]int {
+	lines := strings.Split(input, "\n")
+	allCoords := make([][4]int, len(lines))
+	for i, l := range lines {
+		newCoord := [4]int{}
+		fmt.Sscanf(l, "%d,%d,%d,%d", &newCoord[0], &newCoord[1], &newCoord[2], &newCoord[3])
+
+		allCoords[i] = newCoord
+	}
+
+	return allCoords
+}
+
+func manhattanDistance(one, two [4]int) int {
+	var sum int
+	for i := range one {
+		diff := one[i] - two[i]
+		if diff < 0 {
+			diff *= -1
+		}
+		sum += diff
+	}
+	return sum
+}
diff --git a/2018/day25/main_test.go b/2018/day25/main_test.go
new file mode 100644
index 0000000..b6aa1a0
--- /dev/null
+++ b/2018/day25/main_test.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+var tests1 = []struct {
+	name  string
+	want  int
+	input string
+	// add extra args if needed
+}{
+	{"example 2", 2, `0,0,0,0
+3,0,0,0
+0,3,0,0
+0,0,3,0
+0,0,0,3
+0,0,0,6
+9,0,0,0
+12,0,0,0`},
+	{"example 3", 3, `1,-1,0,1
+2,0,-1,0
+3,2,-1,0
+0,0,3,1
+0,0,-1,-1
+2,3,-2,0
+-2,2,0,0
+2,-2,0,-1
+1,-1,0,-1
+3,2,0,2`},
+	{"example 4", 4, `-1,2,2,0
+0,0,2,-2
+0,0,0,-2
+-1,2,0,0
+-2,-2,-2,2
+3,0,2,-1
+-1,3,2,2
+-1,0,-1,0
+0,2,1,-2
+3,0,0,0`},
+	{"example 8", 8, `1,-1,-1,-2
+-2,-2,0,1
+0,2,1,3
+-2,3,-2,1
+0,2,3,-2
+-1,-1,1,-2
+0,-2,-1,0
+-2,2,3,-1
+1,2,2,0
+-1,-2,0,-2`},
+	{"actual", 422, util.ReadFile("input.txt")},
+}
+
+func TestPart1(t *testing.T) {
+	for _, tt := range tests1 {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := part1(tt.input); got != tt.want {
+				t.Errorf("part1() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}