2023 Day 10 Complete!

2023-12-10 10:26:21 -06:00
parent 433a4414b6
commit be17b84517
8 changed files with 656 additions and 0 deletions
--- a/2023/day10/main.go
+++ b/2023/day10/main.go
@@ -0,0 +1,168 @@
+package main
+
+import (
+	"fmt"
+
+	h "git.bullercodeworks.com/brian/adventofcode/helpers"
+)
+
+func main() {
+	inp := h.StdinToStringSlice()
+	m, l := part1(inp)
+	fmt.Println()
+	part2(m, l)
+}
+
+const (
+	NS = '|'
+	EW = '-'
+	NE = 'L'
+	NW = 'J'
+	SW = '7'
+	SE = 'F'
+
+	START = 'S'
+)
+
+var pipes = []byte{NS, EW, NE, NW, SW, SE}
+
+func part1(input []string) (h.CoordByteMap, []h.Coordinate) {
+	m := h.StringSliceToCoordByteMap(input)
+	_, loop := findLoop(&m)
+	fmt.Println("# Part 1")
+	fmt.Println(len(loop) / 2)
+	return m, loop
+}
+
+func part2(m h.CoordByteMap, loop []h.Coordinate) {
+	var insideCoords []h.Coordinate
+	var inside bool
+	var enclosed int
+	for y := m.TLY; y <= m.BRY; y++ {
+		inside = false
+		var rowPathStart byte
+		for x := m.TLX; x <= m.BRX; x++ {
+			wrk := h.Coordinate{X: x, Y: y}
+			wrkV := m.Get(wrk)
+			if h.CoordListContains(wrk, loop) { //&& (wrkV == NS || wrkV == NE || wrkV == NW) {
+				// This coordinate is part of the loop, so it can change the 'inside' flag
+				// A corner _only_ changes the flag if the 'exiting' corner continues in the same direction
+				// i.e.: L--J doesn't change the flag, L--7 does change the flag
+				switch wrkV {
+				case NE, SE:
+					rowPathStart = wrkV
+				case NW, SW:
+					if continues(rowPathStart, wrkV) {
+						inside = !inside
+					}
+				}
+				if wrkV == NS {
+					// a | always changes the flag
+					inside = !inside
+				}
+			} else {
+				if inside {
+					enclosed++
+					insideCoords = append(insideCoords, wrk)
+				}
+			}
+		}
+	}
+	fmt.Println("# Part 2")
+	fmt.Println(enclosed)
+	for _, insides := range insideCoords {
+		m.Put(insides, 'I')
+	}
+}
+
+// continues checks if two _corner_ pieces continue the flow in the same direction
+func continues(p1, p2 byte) bool {
+	switch p1 {
+	case NE:
+		return p2 == SW
+	case NW:
+		return p2 == SE
+	case SW:
+		return p2 == NE
+	case SE:
+		return p2 == NW
+	}
+	return false
+}
+
+func connectsNorth(v byte) bool {
+	return v == START || v == NS || v == NE || v == NW
+}
+func connectsSouth(v byte) bool {
+	return v == START || v == NS || v == SE || v == SW
+}
+func connectsEast(v byte) bool {
+	return v == START || v == EW || v == NE || v == SE
+}
+func connectsWest(v byte) bool {
+	return v == START || v == EW || v == NW || v == SW
+}
+
+func connects(m *h.CoordByteMap, p1, p2 h.Coordinate) bool {
+	p1v, p2v := m.Get(p1), m.Get(p2)
+	switch {
+	case p1.North().Equals(p2):
+		return connectsNorth(p1v) && connectsSouth(p2v)
+	case p1.East().Equals(p2):
+		return connectsEast(p1v) && connectsWest(p2v)
+	case p1.South().Equals(p2):
+		return connectsSouth(p1v) && connectsNorth(p2v)
+	case p1.West().Equals(p2):
+		return connectsWest(p1v) && connectsEast(p2v)
+	}
+	return false
+}
+
+func countConnections(m *h.CoordByteMap, p h.Coordinate) int {
+	var res int
+	for _, tst := range []h.Coordinate{p.North(), p.East(), p.South(), p.West()} {
+		if connects(m, p, tst) {
+			res++
+		}
+	}
+	return res
+}
+
+// Find loop finds all coordinates on the loop and returns:
+// 1. The starting coordinate
+// 2. All coordinates on the loop
+// It also replaces the 'S' for the starting coordinate with the appropriate
+// pipe byte
+func findLoop(m *h.CoordByteMap) (h.Coordinate, []h.Coordinate) {
+	start, _ := m.FindFirst(START)
+	next := start
+	path := []h.Coordinate{start}
+
+	// Figure out the starting pipe byte
+	for _, v := range pipes {
+		m.Put(start, v)
+		if countConnections(m, start) == 2 {
+			break
+		}
+	}
+
+	for {
+		for _, tst := range []h.Coordinate{
+			next.North(),
+			next.East(),
+			next.South(),
+			next.West(),
+		} {
+			if !connects(m, next, tst) || (!tst.Equals(start) && h.CoordListContains(tst, path)) {
+				continue
+			}
+			next = tst
+		}
+		if next.Equals(start) {
+			// We're done
+			return start, path
+		} else {
+			path = append(path, next)
+		}
+	}
+}