Add solution day 10 part 1

Author: terminalnode

README.md

@@ -54,7 +54,7 @@ automatically rebuilt and redeployed ever time the `common` module or their own
 | 07  | ⭐ ⭐      | 20  |          |
 | 08  | ⭐ ⭐      | 21  |          |
 | 09  |          | 22  |          |
-| 10  |          | 23  |          |
+| 10  | ⭐        | 23  |          |
 | 11  |          | 24  |          |
 | 12  |          | 25  |          |
 | 13  |          |     |          |

solutions/day10/main.go

@@ -1,9 +1,82 @@
 package main
 
 import (
+	"fmt"
 	"github.com/terminalnode/adventofcode2024/common"
+	"github.com/terminalnode/adventofcode2024/common/util"
+	"strings"
 )
 
 func main() {
-	common.Setup(10, nil, nil)
+	common.Setup(10, part1, nil)
+}
+
+func part1(
+	input string,
+) string {
+	topo := parseTopographicMap(input)
+
+	out := 0
+	for y := 0; y < len(topo); y++ {
+		row := topo[y]
+		for x := 0; x < len(row); x++ {
+			value := topo[y][x]
+			if value != 0 {
+				continue
+			}
+
+			nineMap := make(map[string]bool)
+			buildMapForPart1(topo, nineMap, util.Coordinate{X: x, Y: y}, -1)
+			out += len(nineMap)
+		}
+	}
+
+	return fmt.Sprintf("Number of trails: %d", out)
+}
+
+func parseTopographicMap(
+	input string,
+) [][]int {
+	lines := strings.Split(input, "\n")
+	out := make([][]int, len(lines))
+	for y, row := range lines {
+		out[y] = make([]int, len(row))
+		for x, char := range row {
+			digit := int(char) - '0'
+			out[y][x] = digit
+		}
+	}
+
+	return out
+}
+
+func buildMapForPart1(
+	topographicMap [][]int,
+	nineMap map[string]bool,
+	position util.Coordinate,
+	prevValue int,
+) {
+	if !util.In2DArray(position, topographicMap) {
+		return
+	}
+
+	value := topographicMap[position.Y][position.X]
+	if value != prevValue+1 {
+		return
+	}
+
+	if value == 9 {
+		k := fmt.Sprintf("%v", position)
+		nineMap[k] = true
+	} else {
+		cs := []util.Coordinate{
+			position.North(),
+			position.East(),
+			position.South(),
+			position.West(),
+		}
+		for _, newPos := range cs {
+			buildMapForPart1(topographicMap, nineMap, newPos, value)
+		}
+	}
 }