feat(go): add day8

2025/day8/day8.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+type Edge struct {
+	dist int64
+	i, j int
+}
+
+type DSU struct {
+	parent []int
+}
+
+func NewDSU(n int) *DSU {
+	p := make([]int, n)
+	for i := range p {
+		p[i] = i
+	}
+	return &DSU{parent: p}
+}
+
+func (d *DSU) Find(x int) int {
+	if d.parent[x] != x {
+		d.parent[x] = d.Find(d.parent[x])
+	}
+	return d.parent[x]
+}
+
+func (d *DSU) Union(a, b int) {
+	ra := d.Find(a)
+	rb := d.Find(b)
+	if ra != rb {
+		d.parent[ra] = rb
+	}
+}
+
+type Point struct {
+	x, y, z int
+}
+
+func main() {
+	data, _ := os.ReadFile("input.txt")
+	lines := strings.Split(strings.TrimSpace(string(data)), "\n")
+
+	points := []Point{}
+	for _, line := range lines {
+		fields := strings.Split(line, ",")
+		if len(fields) != 3 {
+			continue
+		}
+		x, _ := strconv.Atoi(strings.TrimSpace(fields[0]))
+		y, _ := strconv.Atoi(strings.TrimSpace(fields[1]))
+		z, _ := strconv.Atoi(strings.TrimSpace(fields[2]))
+		points = append(points, Point{x, y, z})
+	}
+
+	n := len(points)
+
+	edges := make([]Edge, 0, n*(n-1)/2)
+	for i := range n {
+		p1 := points[i]
+		for j := range i {
+			p2 := points[j]
+			dx := int64(p1.x - p2.x)
+			dy := int64(p1.y - p2.y)
+			dz := int64(p1.z - p2.z)
+			dist := dx*dx + dy*dy + dz*dz
+			edges = append(edges, Edge{dist, i, j})
+		}
+	}
+
+	sort.Slice(edges, func(a, b int) bool {
+		return edges[a].dist < edges[b].dist
+	})
+
+	dsu := NewDSU(n)
+
+	connections := 0
+
+	for t, e := range edges {
+		if t == 1000 {
+			sz := make(map[int]int)
+			for x := range n {
+				root := dsu.Find(x)
+				sz[root]++
+			}
+
+			list := make([]int, 0, len(sz))
+			for _, v := range sz {
+				list = append(list, v)
+			}
+			sort.Ints(list)
+
+			if len(list) >= 3 {
+				fmt.Println(list[len(list)-1] * list[len(list)-2] * list[len(list)-3])
+			} else {
+				fmt.Println(0)
+			}
+		}
+
+		ri := dsu.Find(e.i)
+		rj := dsu.Find(e.j)
+		if ri != rj {
+			connections++
+			if connections == n-1 {
+				fmt.Println(points[e.i].x * points[e.j].x)
+			}
+			dsu.Union(ri, rj)
+		}
+	}
+}

2025/day8/go.mod

@@ -0,0 +1,3 @@
+module day8
+
+go 1.23.4