AoC 2020: day4

Signed-off-by: Ettore Dreucci <ettore.dreucci@gmail.com>

2019-go/day_03/day_03.go

@@ -0,0 +1,120 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"math"
+	"os"
+	"strconv"
+	"strings"
+
+	mapset "github.com/deckarep/golang-set"
+)
+
+type point struct {
+	x int
+	y int
+}
+
+func readValues(fileName string) [][]string {
+	file, err := os.Open(fileName)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	values := make([][]string, 0)
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		lineElements := strings.Split(scanner.Text(), ",")
+		values = append(values, lineElements)
+	}
+	return values
+}
+
+func wireTrace(cableMoves []string) ([]point, mapset.Set) {
+	currentPosition := point{0, 0}
+	cablePath := make([]point, 0)
+	cableSet := mapset.NewSet()
+	for _, step := range cableMoves {
+		direction := step[0]
+		distance, err := strconv.Atoi(string(step[1:]))
+		if err != nil {
+			log.Fatalf("Cannot decode step lenght: %c\n", step[1])
+		}
+		for i := 0; i < distance; i++ {
+			switch direction {
+			case 'U':
+				currentPosition.y++
+			case 'D':
+				currentPosition.y--
+			case 'R':
+				currentPosition.x++
+			case 'L':
+				currentPosition.x--
+			default:
+				log.Fatalf("Cannot decode step direction: %c\n", direction)
+			}
+			cablePath = append(cablePath, currentPosition)
+			cableSet.Add(currentPosition)
+		}
+	}
+	return cablePath, cableSet
+}
+
+func (p1 point) manhattanDistance(p2 point) int {
+	return int(math.Abs(float64(p1.x-p2.x)) + math.Abs(float64(p1.y-p2.y)))
+}
+
+func reachIntersect(cablePath []point, intersect point) int {
+	for i, pos := range cablePath {
+		if pos.x == intersect.x && pos.y == intersect.y {
+			return i + 1
+		}
+	}
+	return -1
+}
+
+func shortestDistance(intersectionPoints mapset.Set) int {
+	origin := point{0, 0}
+	bestDistance := 0
+	for p := range intersectionPoints.Iterator().C {
+		dist := origin.manhattanDistance(p.(point))
+		if bestDistance == 0 || dist < bestDistance {
+			bestDistance = dist
+		}
+	}
+	return bestDistance
+}
+
+func fewestSteps(cablesPath [][]point, intersectionPoints mapset.Set) int {
+	bestSteps := 0
+	for p := range intersectionPoints.Iterator().C {
+		steps := reachIntersect(cablesPath[0], p.(point)) + reachIntersect(cablesPath[1], p.(point))
+		if bestSteps == 0 || steps < bestSteps {
+			bestSteps = steps
+		}
+	}
+	return bestSteps
+}
+
+func main() {
+	cablesMoves := readValues("./input")
+	cable1Path, cable1Set := wireTrace(cablesMoves[0])
+	cable2Path, cable2Set := wireTrace(cablesMoves[1])
+
+	intersectionPoints := cable1Set.Intersect(cable2Set)
+	if intersectionPoints.Cardinality() == 0 {
+		log.Fatalln("No intersection point")
+	}
+
+	// Part 1
+	dist := shortestDistance(intersectionPoints)
+	fmt.Printf("Part 1: %d\n", dist)
+
+	//Part 2
+	steps := fewestSteps([][]point{cable1Path, cable2Path}, intersectionPoints)
+	fmt.Printf("Part 2: %d\n", steps)
+}