✨Added Day 9 Solution

Day 9/README.md

@@ -0,0 +1,78 @@
+# Day 9: Smoke Basin
+
+These caves seem to be [lava tubes](https://en.wikipedia.org/wiki/Lava_tube). Parts are even still volcanically active; small hydrothermal vents release smoke into the caves that slowly settles like rain.
+
+If you can model how the smoke flows through the caves, you might be able to avoid it and be that much safer. The submarine generates a heightmap of the floor of the nearby caves for you (your puzzle input).
+
+Smoke flows to the lowest point of the area it's in. For example, consider the following heightmap:
+
+```
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
+```
+
+Each number corresponds to the height of a particular location, where `9` is the highest and `0` is the lowest a location can be.
+
+Your first goal is to find the **low points** - the locations that are lower than any of its adjacent locations. Most locations have four adjacent locations (up, down, left, and right); locations on the edge or corner of the map have three or two adjacent locations, respectively. (Diagonal locations do not count as adjacent.)
+
+In the above example, there are **four** low points, all highlighted: two are in the first row (a `1` and a `0`), one is in the third row (a `5`), and one is in the bottom row (also a `5`). All other locations on the heightmap have some lower adjacent location, and so are not low points.
+
+The **risk level** of a low point is **1 plus its height**. In the above example, the risk levels of the low points are `2`, `1`, `6`, and `6`. The sum of the risk levels of all low points in the heightmap is therefore `15`.
+
+Find all of the low points on your heightmap. **What is the sum of the risk levels of all low points on your heightmap?**
+
+# Part Two
+
+Next, you need to find the largest basins so you know what areas are most important to avoid.
+
+A **basin** is all locations that eventually flow downward to a single low point. Therefore, every low point has a basin, although some basins are very small. Locations of height `9` do not count as being in any basin, and all other locations will always be part of exactly one basin.
+
+The **size** of a basin is the number of locations within the basin, including the low point. The example above has four basins.
+
+The top-left basin, size `3`:
+
+```
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
+```
+
+The top-right basin, size `9`:
+
+```
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
+```
+
+The middle basin, size `14`:
+
+```
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
+```
+
+The bottom-right basin, size `9`:
+
+```
+2199943210
+3987894921
+9856789892
+8767896789
+9899965678
+```
+
+Find the three largest basins and multiply their sizes together. In the above example, this is `9 * 14 * 9 = 1134`.
+
+**What do you get if you multiply together the sizes of the three largest basins?**
+

Day 9/input

@@ -0,0 +1,100 @@
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Day 9/main.go

@@ -0,0 +1,108 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+)
+
+func partOne(heightmap [][]uint8) {
+	riskLevel := 0
+	for y, _ := range heightmap {
+		for x, _ := range heightmap[y] {
+			if (y-1 >= 0 && heightmap[y][x] >= heightmap[y-1][x]) ||
+				(y+1 <= len(heightmap)-1 && heightmap[y][x] >= heightmap[y+1][x]) ||
+				(x-1 >= 0 && heightmap[y][x] >= heightmap[y][x-1]) ||
+				(x+1 <= len(heightmap[y])-1 && heightmap[y][x] >= heightmap[y][x+1]) {
+				continue
+			}
+
+			riskLevel += int(heightmap[y][x]) + 1
+		}
+	}
+
+	fmt.Printf("Part One Answer: %d\n", riskLevel)
+}
+
+func getBasinSize(heightmap [][]uint8, basinMap [][]bool, x int, y int) int {
+	basinMap[y][x] = true
+	basinSize := 1
+
+	if x-1 >= 0 && heightmap[y][x-1] != 9 && !basinMap[y][x-1] {
+		basinSize += getBasinSize(heightmap, basinMap, x-1, y)
+	}
+
+	if x+1 <= len(heightmap[y]) - 1 && heightmap[y][x+1] != 9 && !basinMap[y][x+1] {
+		basinSize += getBasinSize(heightmap, basinMap, x+1, y)
+	}
+
+	if y-1 >= 0 && heightmap[y-1][x] != 9 && !basinMap[y-1][x] {
+		basinSize += getBasinSize(heightmap, basinMap, x, y-1)
+	}
+
+	if y+1 <= len(heightmap) - 1 && heightmap[y+1][x] != 9 && !basinMap[y+1][x] {
+		basinSize += getBasinSize(heightmap, basinMap, x, y+1)
+	}
+
+	return basinSize
+}
+
+func partTwo(heightmap [][]uint8) {
+	basinMap := make([][]bool, len(heightmap))
+	for basinIndex, _ := range basinMap {
+		basinMap[basinIndex] = make([]bool, len(heightmap[0]))
+	}
+
+	basins := []int{}
+	for y, _ := range heightmap {
+		for x, _ := range heightmap[y] {
+			if heightmap[y][x] == 9 || basinMap[y][x] {
+				continue
+			}
+
+			basinSize := getBasinSize(heightmap, basinMap, x, y)
+
+			basins = append(basins, basinSize)
+		}
+	}
+
+	sort.Ints(basins)
+	
+	fmt.Printf("Part Two Answer: %d\n", basins[len(basins) - 1] * basins[len(basins) - 2] * basins[len(basins) - 3])
+}
+
+func main() {
+	file, err := os.Open("./input")
+	if err != nil {
+		fmt.Printf("[Error] Unable to open file")
+		os.Exit(1)
+	}
+	defer file.Close()
+
+	heightmap := [][]uint8{}
+	y := 0
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		rowString := scanner.Text()
+		if len(rowString) == 0 {
+			continue
+		}
+
+		heightmap = append(heightmap, make([]uint8, len(rowString)))
+		for x, heightCharacter := range rowString {
+			height, err := strconv.Atoi(string(heightCharacter))
+			if err != nil {
+				fmt.Printf("[Error] Invalid height")
+				continue
+			}
+			heightmap[y][x] = uint8(height)
+		}
+
+		y += 1
+	}
+
+	partOne(heightmap)
+	partTwo(heightmap)
+}