Advent of Code 2023 - Day 18 (#38)

advent_of_code/2023/day18.go

@@ -0,0 +1,98 @@
+package adventofcode
+
+import (
+	"strconv"
+	"strings"
+
+	"golang.org/x/exp/slices"
+)
+
+func day18Part1(input []string) int {
+	// prepare a grid as input, lets assume maximum length is 500
+
+	var (
+		gridRow    = 1000
+		gridColumn = 1000
+		startX     = 300
+		startY     = 300
+	)
+	matrix := make([][]byte, gridRow)
+	for i := 0; i < len(matrix); i++ {
+		matrix[i] = make([]byte, gridColumn)
+	}
+
+	matrix[startX][startY] = '#'
+
+	for _, line := range input {
+		parsedInput := strings.Fields(line)
+
+		// do not need to handle trench color in p1
+		dir := parsedInput[0]
+		length, _ := strconv.Atoi(parsedInput[1])
+
+		for i := 0; i < length; i++ {
+			switch dir {
+			case "R":
+				startY += 1
+			case "D":
+				startX += 1
+			case "U":
+				startX -= 1
+			case "L":
+				startY -= 1
+			}
+			matrix[startX][startY] = '#'
+		}
+	}
+
+	// Next need to dig out the interior area
+	index := 1
+	indexArray := []byte{}
+	for i := 0; i < len(matrix); i++ {
+		for j := 0; j < len(matrix[0]); j++ {
+			if matrix[i][j] == 0 {
+				if traverse18(matrix, byte(index), i, j) {
+					indexArray = append(indexArray, byte(index))
+				}
+				index += 1
+			}
+		}
+	}
+	// we have filled all the array we want, now recalculate
+	res := 0
+	for i := 0; i < len(matrix); i++ {
+		for j := 0; j < len(matrix[0]); j++ {
+			if matrix[i][j] == '#' || slices.Contains(indexArray, matrix[i][j]) {
+				res += 1
+			}
+		}
+	}
+	return res
+}
+
+// bool will return whether it's inside the trench or outside
+func traverse18(grid [][]byte, ch byte, x int, y int) bool {
+	if x < 0 || x > len(grid)-1 || y < 0 || y > len(grid[0])-1 {
+		return false
+	}
+	if (grid[x][y]) == '#' {
+		return true
+	}
+	// this has been visited in the past
+	if grid[x][y] != 0 {
+		return true
+	}
+
+	// mark this has been visited
+	grid[x][y] = ch
+	isInsideTrench := true
+	indexes := []location{location{-1, 0}, location{1, 0}, location{0, -1}, location{0, 1}}
+	for _, idx := range indexes {
+		// well, should traverse firstly and then judge
+		// if use isInsideTrench && traverse18(grid, ch, x+idx.x, y+idx.y)
+		// then many directions won't be explored, still work but cause a waste of time
+		isInsideTrench = traverse18(grid, ch, x+idx.x, y+idx.y) && isInsideTrench
+
+	}
+	return isInsideTrench
+}