Solve 2024 day 6 in go

2024/go/day-06/main.go

@@ -0,0 +1,141 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+type position struct {
+	row int
+	col int
+}
+
+type state struct {
+	row       int
+	col       int
+	direction int
+}
+
+const (
+	up    = 0
+	right = 1
+	down  = 2
+	left  = 3
+)
+
+func readInput() (area [][]rune, start state, err error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+	area = make([][]rune, len(lines))
+
+	for rowIndex, line := range lines {
+		for colIndex, symbol := range line {
+			if symbol == '^' {
+				start = state{row: rowIndex, col: colIndex, direction: up}
+			}
+		}
+
+		area[rowIndex] = []rune(line)
+	}
+
+	return
+}
+
+func stateToPos(s state) position {
+	return position{s.row, s.col}
+}
+
+func isOutOfBounds(area [][]rune, pos position) bool {
+	return (pos.row < 0 || pos.row >= len(area)) || (pos.col < 0 || pos.col >= len(area[0]))
+}
+
+func isObstacle(area [][]rune, pos position) bool {
+	return area[pos.row][pos.col] == '#'
+}
+
+func takeStep(area [][]rune, currentState state) (bool, state) {
+	directions := map[int]position{up: {-1, 0}, right: {0, 1}, down: {1, 0}, left: {0, -1}}
+
+	newState := state{
+		row:       currentState.row + directions[currentState.direction].row,
+		col:       currentState.col + directions[currentState.direction].col,
+		direction: currentState.direction,
+	}
+
+	if isOutOfBounds(area, stateToPos(newState)) {
+		return false, newState
+	}
+
+	if isObstacle(area, stateToPos(newState)) {
+		currentState.direction = (currentState.direction + 1) % 4
+		return true, currentState
+	}
+
+	return true, newState
+}
+
+func findDistinctPositions(area [][]rune, currentState state) map[position]bool {
+	distinctPositions := make(map[position]bool)
+
+	for ok := true; ok; {
+		distinctPositions[stateToPos(currentState)] = true
+
+		ok, currentState = takeStep(area, currentState)
+	}
+
+	return distinctPositions
+}
+
+func isLoopCausingObstruction(area [][]rune, currentState state) bool {
+	path := make(map[state]bool)
+
+	for ok := true; ok; {
+		if _, isLoop := path[currentState]; isLoop {
+			return true
+		}
+		path[currentState] = true
+
+		ok, currentState = takeStep(area, currentState)
+	}
+
+	return false
+}
+
+func findLoopCausingObstructions(area [][]rune, start state, distinctPositions map[position]bool) []position {
+	var loopObstructions []position
+
+	for obstaclePos := range distinctPositions {
+		if obstaclePos == stateToPos(start) {
+			continue
+		}
+
+		area[obstaclePos.row][obstaclePos.col] = '#'
+		if isLoopCausingObstruction(area, start) {
+			loopObstructions = append(loopObstructions, obstaclePos)
+		}
+		area[obstaclePos.row][obstaclePos.col] = '.'
+	}
+
+	return loopObstructions
+}
+
+func main() {
+	area, start, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	distinctPositions := findDistinctPositions(area, start)
+	loopObstructions := findLoopCausingObstructions(area, start, distinctPositions)
+
+	// Part one
+	fmt.Println("Number of distinct positions:", len(distinctPositions))
+	// Part two
+	fmt.Println("Number of potential obstructions:", len(loopObstructions))
+}