From 070c03e6631e961dbcd9ce521df4c65ab94d467f Mon Sep 17 00:00:00 2001
From: Abel Tay <15604207+abeltay@users.noreply.github.com>
Date: Wed, 27 Dec 2023 22:51:05 +0800
Subject: [PATCH] Day 25: Snowverload

---
 25/main.go           | 163 +++++++++++++++++++++++++++++++++++++++++++
 25/main_test.go      |  19 +++++
 25/testdata/test.txt |  13 ++++
 3 files changed, 195 insertions(+)
 create mode 100644 25/main.go
 create mode 100644 25/main_test.go
 create mode 100644 25/testdata/test.txt

diff --git a/25/main.go b/25/main.go
new file mode 100644
index 0000000..d89f603
--- /dev/null
+++ b/25/main.go
@@ -0,0 +1,163 @@
+package main
+
+import (
+	"math/rand"
+	"sort"
+	"strings"
+
+	"github.com/abeltay/advent-of-code-2023/utilities"
+)
+
+func parseInput(filename string) [][]bool {
+	in := utilities.ParseFile(filename)
+
+	all := make(map[string]bool)
+	for _, row := range in {
+		s := strings.Split(row, ": ")
+		all[s[0]] = true
+		for _, v := range strings.Split(s[1], " ") {
+			all[v] = true
+		}
+	}
+	names := make([]string, 0, len(all))
+	for k := range all {
+		names = append(names, k)
+	}
+	sort.Strings(names)
+	connections := make([][]bool, len(names))
+	for i := range names {
+		connections[i] = make([]bool, len(names))
+	}
+	for _, row := range in {
+		s := strings.Split(row, ": ")
+		from := sort.SearchStrings(names, s[0])
+		for _, v := range strings.Split(s[1], " ") {
+			to := sort.SearchStrings(names, v)
+			connections[from][to] = true
+			connections[to][from] = true
+		}
+	}
+	return connections
+}
+
+type node struct {
+	num    int
+	parent *node
+}
+
+func bfs(connections [][]bool, breaks []connect, from, to int) *node {
+	visited := make([]bool, len(connections))
+	visited[from] = true
+	queue := []node{{num: from}}
+	for len(queue) > 0 {
+		last := queue[0]
+		queue = queue[1:]
+		if last.num == to {
+			return &last
+		}
+		for i := range connections[last.num] {
+			if !connections[last.num][i] || visited[i] {
+				continue
+			}
+			var broken bool
+			for _, v := range breaks {
+				if v.from == last.num && v.to == i {
+					broken = true
+				}
+			}
+			if broken {
+				continue
+			}
+			visited[i] = true
+			queue = append(queue, node{num: i, parent: &last})
+		}
+	}
+	return nil
+}
+
+type connect struct {
+	from int
+	to   int
+}
+
+func connectedAfter3Breaks(connections [][]bool, from, to int) []connect {
+	var breaks []connect
+	for i := 0; i < 3; i++ {
+		path := bfs(connections, breaks, from, to)
+		from := path.num
+		next := path.parent
+		for next != nil {
+			breaks = append(breaks, connect{from, next.num})
+			breaks = append(breaks, connect{next.num, from})
+			from = next.num
+			next = next.parent
+		}
+	}
+	path := bfs(connections, breaks, from, to)
+	if path != nil {
+		return nil
+	}
+	return breaks
+}
+
+func findSize(connections [][]bool, breaks []connect, from int) int {
+	visited := make([]bool, len(connections))
+	visited[from] = true
+	queue := []node{{num: from}}
+	for len(queue) > 0 {
+		last := queue[0]
+		queue = queue[1:]
+		for i := range connections[last.num] {
+			if !connections[last.num][i] || visited[i] {
+				continue
+			}
+			var broken bool
+			for _, v := range breaks {
+				if v.from == last.num && v.to == i {
+					broken = true
+					break
+				}
+			}
+			if broken {
+				continue
+			}
+			visited[i] = true
+			queue = append(queue, node{num: i, parent: &last})
+		}
+	}
+	var count int
+	for _, v := range visited {
+		if v {
+			count++
+		}
+	}
+	return count
+}
+
+func part1(filename string) int {
+	connected := parseInput(filename)
+	sameGroup := []int{0}
+	source := 0
+	r := rand.New(rand.NewSource(99))
+	var breaks []connect
+	for {
+		n := int(r.Int31n(int32(len(connected))))
+		var exists bool
+		for _, v := range sameGroup {
+			if v == n {
+				exists = true
+				break
+			}
+		}
+		if exists {
+			continue
+		}
+		breaks = connectedAfter3Breaks(connected, source, n)
+		if breaks != nil {
+			break
+		}
+		sameGroup = append(sameGroup, n)
+	}
+	size := findSize(connected, breaks, 0)
+	return size * (len(connected) - size)
+}
diff --git a/25/main_test.go b/25/main_test.go
new file mode 100644
index 0000000..45d1995
--- /dev/null
+++ b/25/main_test.go
@@ -0,0 +1,19 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestParts(t *testing.T) {
+	testFile := "testdata/test.txt"
+	got := part1(testFile)
+	want := 54
+	if got != want {
+		t.Fatalf("got %v want %v", got, want)
+	}
+
+	fmt.Println("Running input.txt")
+	actualFile := "testdata/input.txt"
+	fmt.Println("Answer for part 1:", part1(actualFile))
+}
diff --git a/25/testdata/test.txt b/25/testdata/test.txt
new file mode 100644
index 0000000..bbfda0b
--- /dev/null
+++ b/25/testdata/test.txt
@@ -0,0 +1,13 @@
+jqt: rhn xhk nvd
+rsh: frs pzl lsr
+xhk: hfx
+cmg: qnr nvd lhk bvb
+rhn: xhk bvb hfx
+bvb: xhk hfx
+pzl: lsr hfx nvd
+qnr: nvd
+ntq: jqt hfx bvb xhk
+nvd: lhk
+lsr: lhk
+rzs: qnr cmg lsr rsh
+frs: qnr lhk lsr