1 files changed, 89 insertions(+), 0 deletions(-)

A d22/main.go

@@ 0,0 1,89 @@
+package main
+
+import (
+	"strconv"
+	"strings"
+)
+
+type Point struct {
+	X int
+	Y int
+}
+
+type RegionType int
+
+const (
+	RegionTypeRocky RegionType = iota
+	RegionTypeWet
+	RegionTypeNarrow
+)
+
+type Cave struct {
+	Depth  int
+	Target Point
+
+	gidxCache map[Point]int
+	elvlCache map[Point]int
+}
+
+func (c Cave) GeoIndex(p Point) (idx int) {
+	if idx, ok := c.gidxCache[p]; ok {
+		return idx
+	}
+	switch {
+	case p == Point{} || p == c.Target:
+		idx = 0
+	case p.Y == 0:
+		idx = p.X * 16807
+	case p.X == 0:
+		idx = p.Y * 48271
+	default:
+		idx = c.ErosionLevel(pt(p.X-1, p.Y)) *
+			c.ErosionLevel(pt(p.X, p.Y-1))
+	}
+	c.gidxCache[p] = idx
+	return
+}
+
+func (c Cave) ErosionLevel(p Point) (lvl int) {
+	if lvl, ok := c.elvlCache[p]; ok {
+		return lvl
+	}
+	lvl = (c.GeoIndex(p) + c.Depth) % 20183
+	c.elvlCache[p] = lvl
+	return
+}
+
+func (c Cave) RegionType(p Point) RegionType {
+	return RegionType(c.ErosionLevel(p) % 3)
+}
+
+func pt(x, y int) Point {
+	return Point{X: x, Y: y}
+}
+
+func parseInput(in chan string) (cave Cave, target Point) {
+	cave = Cave{
+		Depth:     mustAtoi((<-in)[7:]),
+		gidxCache: make(map[Point]int),
+		elvlCache: make(map[Point]int),
+	}
+	tc := strings.Split((<-in)[8:], ",")
+	target = Point{
+		X: mustAtoi(tc[0]),
+		Y: mustAtoi(tc[1]),
+	}
+	cave.Target = target
+	return
+}
+
+func task1(in chan string) string {
+	c, target := parseInput(in)
+	riskLevel := 0
+	for x := 0; x <= target.X; x++ {
+		for y := 0; y <= target.Y; y++ {
+			riskLevel += int(c.RegionType(pt(x, y)))
+		}
+	}
+	return strconv.Itoa(riskLevel)
+}