add day03 solution.

Author: lizthegrey

2023/day03.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"strings"
+)
+
+var inputFile = flag.String("inputFile", "inputs/day03.input", "Relative file path to use as input.")
+
+type Coord struct {
+	X, Y int
+}
+
+func main() {
+	flag.Parse()
+	bytes, err := ioutil.ReadFile(*inputFile)
+	if err != nil {
+		return
+	}
+	contents := string(bytes)
+	split := strings.Split(contents, "\n")
+
+	sum := 0
+	grid := make(map[Coord]rune)
+	gears := make(map[Coord][]int)
+	var maxX, maxY int
+	for y, row := range split[:len(split)-1] {
+		for x, c := range row {
+			grid[Coord{x, y}] = c
+			if x > maxX {
+				maxX = x
+			}
+		}
+		if y > maxY {
+			maxY = y
+		}
+	}
+	for y := 0; y <= maxY; y++ {
+		for x := 0; x <= maxX; {
+			c := grid[Coord{x, y}]
+			if c < '0' || c > '9' {
+				x++
+				continue
+			}
+			// We've found a number. Keep reading to the right.
+			num := int(c - '0')
+			length := 1
+			for i := 1; ; i++ {
+				n := grid[Coord{x + i, y}]
+				if n < '0' || n > '9' {
+					break
+				}
+				num = 10*num + int(n-'0')
+				length++
+			}
+		outer:
+			for j := y - 1; j <= y+1; j++ {
+				for i := x - 1; i <= x+length; i++ {
+					nCoord := Coord{i, j}
+					neigh := grid[nCoord]
+					if neigh == 0 || neigh == '.' {
+						continue
+					}
+					if neigh >= '0' && neigh <= '9' {
+						continue
+					}
+					sum += num
+					if neigh == '*' {
+						gears[nCoord] = append(gears[nCoord], num)
+					}
+					break outer
+				}
+			}
+			x = x + length
+		}
+	}
+	fmt.Println(sum)
+
+	ratio := 0
+	for _, v := range gears {
+		if len(v) == 2 {
+			ratio += v[0] * v[1]
+		}
+	}
+	fmt.Println(ratio)
+}