add day25a solution.

Author: lizthegrey

2018/day25.go

@@ -0,0 +1,116 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var inputFile = flag.String("inputFile", "inputs/day25.input", "Relative file path to use as input.")
+
+type Coord4 struct {
+	X, Y, Z, T int
+}
+
+func (c Coord4) Adjacent(t Coord4) bool {
+	deltaX := c.X - t.X
+	deltaY := c.Y - t.Y
+	deltaZ := c.Z - t.Z
+	deltaT := c.T - t.T
+
+	sum := 0
+	if deltaX < 0 {
+		sum -= deltaX
+	} else {
+		sum += deltaX
+	}
+	if deltaY < 0 {
+		sum -= deltaY
+	} else {
+		sum += deltaY
+	}
+	if deltaZ < 0 {
+		sum -= deltaZ
+	} else {
+		sum += deltaZ
+	}
+	if deltaT < 0 {
+		sum -= deltaT
+	} else {
+		sum += deltaT
+	}
+
+	return sum <= 3
+}
+
+func main() {
+	flag.Parse()
+	f, err := os.Open(*inputFile)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	coords := make([]Coord4, 0)
+	r := bufio.NewReader(f)
+	for {
+		l, err := r.ReadString('\n')
+		if err != nil || len(l) == 0 {
+			break
+		}
+		l = l[:len(l)-1]
+		nums := strings.Split(l, ",")
+		x, _ := strconv.Atoi(nums[0])
+		y, _ := strconv.Atoi(nums[1])
+		z, _ := strconv.Atoi(nums[2])
+		t, _ := strconv.Atoi(nums[3])
+		coords = append(coords, Coord4{x, y, z, t})
+	}
+
+	// Maps index of coord to clique number.
+	cliquesByCoord := make(map[int]int)
+	coordsByClique := make(map[int][]int)
+
+	// Seed the first element.
+	highestClique := 1
+
+	changed := true
+	for changed {
+		changed = false
+		for c := range coords {
+			cClique := cliquesByCoord[c]
+			if cClique == 0 {
+				cliquesByCoord[c] = highestClique
+				coordsByClique[highestClique] = []int{c}
+				cClique = highestClique
+				highestClique++
+				changed = true
+			}
+			for t := range coords {
+				tClique := cliquesByCoord[t]
+				if tClique == cClique {
+					continue
+				}
+				if coords[c].Adjacent(coords[t]) {
+					if tClique == 0 {
+						cliquesByCoord[t] = cClique
+						coordsByClique[cClique] = append(coordsByClique[cClique], t)
+						changed = true
+						continue
+					}
+					// Merge the t Clique and the c Clique.
+					changed = true
+					for _, v := range coordsByClique[tClique] {
+						cliquesByCoord[v] = cClique
+					}
+					coordsByClique[cClique] = append(coordsByClique[cClique], coordsByClique[tClique]...)
+					delete(coordsByClique, tClique)
+				}
+			}
+		}
+	}
+	fmt.Println(len(coordsByClique))
+}