starting 2023

2023/day03/main.go

@@ -0,0 +1,198 @@
+package main
+
+import (
+	_ "embed"
+	"flag"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/alexchao26/advent-of-code-go/cast"
+	"github.com/alexchao26/advent-of-code-go/util"
+)
+
+//go:embed input.txt
+var input string
+
+func init() {
+	// do this in init (not main) so test file has same input
+	input = strings.TrimRight(input, "\n")
+	if len(input) == 0 {
+		panic("empty input.txt file")
+	}
+}
+
+func main() {
+	var part int
+	flag.IntVar(&part, "part", 1, "part 1 or 2")
+	flag.Parse()
+	fmt.Println("Running part", part)
+
+	if part == 1 {
+		ans := part1(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	} else {
+		ans := part2(input)
+		util.CopyToClipboard(fmt.Sprintf("%v", ans))
+		fmt.Println("Output:", ans)
+	}
+}
+
+var numReg = regexp.MustCompile("[0-9]")
+
+func part1(input string) int {
+	matrix := [][]string{}
+
+	// collect special characters
+	specialChars := map[string]bool{}
+	for _, row := range strings.Split(input, "\n") {
+		matrix = append(matrix, strings.Split(row, ""))
+		for _, val := range strings.Split(row, "") {
+			if !numReg.MatchString(val) && val != "." {
+				specialChars[val] = true
+			}
+		}
+	}
+	specialCharsString := ""
+	for k := range specialChars {
+		specialCharsString += k
+	}
+
+	var sum int
+
+	diffs := [8][2]int{
+		{-1, -1},
+		{-1, 0},
+		{-1, 1},
+		{0, -1},
+		{0, 1},
+		{1, -1},
+		{1, 0},
+		{1, 1},
+	}
+
+	seen := map[[2]int]bool{}
+	for r, row := range matrix {
+		for c, val := range row {
+			coords := [2]int{r, c}
+			if seen[coords] {
+				continue
+			}
+			seen[coords] = true
+
+			// if we hit a number, collect the entire number and check along the way if it's
+			// adjacent to a special char
+			if numReg.MatchString(val) {
+				hasAdjacentSpecialChar := false
+
+				numStr := ""
+				for j := 0; j+c < len(matrix[0]); j++ {
+					char := row[c+j]
+					// breaks on period or special character, loop itself breaks on out of range
+					if !numReg.MatchString(char) {
+						break
+					}
+					// keep collecting number
+					numStr += char
+
+					// check all 8 directions for special char
+					for _, d := range diffs {
+						dr, dc := r+d[0], c+j+d[1]
+						if dr >= 0 && dr < len(matrix) && dc >= 0 && dc < len(matrix[0]) {
+							if strings.ContainsAny(matrix[dr][dc], specialCharsString) {
+								hasAdjacentSpecialChar = true
+							}
+							seen[[2]int{r, c + j}] = true
+						}
+					}
+				}
+
+				if hasAdjacentSpecialChar {
+					sum += cast.ToInt(numStr)
+				}
+
+			}
+		}
+	}
+
+	return sum
+}
+
+// getNumber returns -1 if a number is "not found" which could include the number
+// already being seen
+func getNumber(matrix [][]string, coord [2]int, seen map[[2]int]bool) int {
+	if !numReg.MatchString(matrix[coord[0]][coord[1]]) {
+		return -1
+	}
+	if seen[coord] {
+		return -1
+	}
+	// go to the left most digit
+	r, c := coord[0], coord[1]
+	for c-1 >= 0 {
+		if numReg.MatchString(matrix[r][c-1]) {
+			c--
+		} else {
+			break
+		}
+	}
+
+	numStr := ""
+
+	for c < len(matrix[0]) && numReg.MatchString(matrix[r][c]) {
+		numStr += matrix[r][c]
+		seen[[2]int{r, c}] = true
+		c++
+	}
+
+	return cast.ToInt(numStr)
+}
+
+func part2(input string) int {
+	// lucky edge case that there are not multiple gears that share the same number such as
+	// ....*....
+	// .123.456.   OR    ...123*456*789...
+	// ....*....
+	// with the current useage of "seen", this would only get counted once
+	seen := map[[2]int]bool{}
+
+	matrix := [][]string{}
+	for _, row := range strings.Split(input, "\n") {
+		matrix = append(matrix, strings.Split(row, ""))
+	}
+
+	diffs := [8][2]int{
+		{-1, -1},
+		{-1, 0},
+		{-1, 1},
+		{0, -1},
+		{0, 1},
+		{1, -1},
+		{1, 0},
+		{1, 1},
+	}
+
+	sum := 0
+	for r, rows := range matrix {
+		for c, val := range rows {
+			if val == "*" {
+				nums := []int{}
+				for _, diff := range diffs {
+					dr, dc := r+diff[0], c+diff[1]
+					if dr >= 0 && dr < len(matrix) && dc >= 0 && dc < len(matrix[0]) {
+						foundNum := getNumber(matrix, [2]int{dr, dc}, seen)
+						if foundNum != -1 {
+							nums = append(nums, foundNum)
+						}
+					}
+				}
+
+				if len(nums) == 2 {
+					sum += nums[0] * nums[1]
+				}
+			}
+		}
+	}
+	return sum
+}