2021 Day 9 Complete!

2021/day09/main.go

@@ -0,0 +1,96 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	m := h.StringSliceToCoordByteMap(inp)
+
+	findBasins(m, findLowestPoints(m))
+}
+
+func findLowestPoints(m h.CoordByteMap) []h.Coordinate {
+	var points []h.Coordinate
+	var low []int
+	for y := 0; y < m.Height; y++ {
+		for x := 0; x < m.Width; x++ {
+			c := h.Coordinate{X: x, Y: y}
+			v := m.Get(c)
+			if y > 0 { // Check North
+				if m.Get(c.North()) <= v {
+					continue
+				}
+			}
+			if y < m.Height-1 { // Check South
+				if m.Get(c.South()) <= v {
+					continue
+				}
+			}
+			if x > 0 { // Check West
+				if m.Get(c.West()) <= v {
+					continue
+				}
+			}
+			if x < m.Width-1 { // Check East
+				if m.Get(c.East()) <= v {
+					continue
+				}
+			}
+			points = append(points, c)
+			low = append(low, btoi(v))
+		}
+	}
+	fmt.Println()
+	fmt.Println("# Part 1")
+	var tot int
+	for i := range low {
+		tot += low[i] + 1
+	}
+	fmt.Println("Total Risk Level:", tot)
+	return points
+}
+
+func findBasins(m h.CoordByteMap, lows []h.Coordinate) {
+	basins := make(map[h.Coordinate]int)
+	for i := range lows {
+		basins[lows[i]], _ = findBasinSize(m, lows[i], make(map[h.Coordinate]bool))
+	}
+	// Find the three largest
+	one := h.MIN_INT
+	two := h.MIN_INT
+	three := h.MIN_INT
+	for _, v := range basins {
+		if v > one {
+			one, two, three = v, one, two
+		} else if v > two {
+			two, three = v, two
+		} else if v > three {
+			three = v
+		}
+	}
+	fmt.Println()
+	fmt.Println("# Part 2")
+	fmt.Println("Total:", (one * two * three))
+}
+
+func findBasinSize(m h.CoordByteMap, low h.Coordinate, checked map[h.Coordinate]bool) (int, map[h.Coordinate]bool) {
+	size := 1
+	checked[low] = true
+	for _, v := range []h.Coordinate{low.North(), low.East(), low.South(), low.West()} {
+		if m.Get(v) != 0 && !checked[v] && btoi(m.Get(v)) < 9 {
+			var s int
+			s, checked = findBasinSize(m, v, checked)
+			size += s
+		}
+	}
+
+	return size, checked
+}
+
+func btoi(b byte) int {
+	return int(b) - 48
+}