aoc2023/day-10/one.go

package main

import (
	log "github.com/sirupsen/logrus"
)

type coords struct {
	X int
	Y int
}

type points struct {
	points []point
}

type point struct {
	N bool
	S bool
	E bool
	W bool
	coords
	identifier rune
}

var pointsArray = []points{}

type tracker struct {
	init  point
	point point
	last  []coords
	steps int
}

// newTracker stores the starting point
// it creates a queue for storing past 2 moves
// returns a tracker struct for counting steps
func newTracker() tracker {
	tracker := tracker{last: make([]coords, 0)}
	for _, each := range pointsArray {
		for _, point := range each.points {
			if point.identifier == 'S' {
				tracker.init = point
				tracker.point = tracker.init
				tracker.last = make([]coords, 1)
				tracker.last = append(tracker.last, tracker.point.coords)
			}
		}
	}
	return tracker
}

func (t tracker) X() int {
	return t.point.X
}

func (t tracker) Y() int {
	return t.point.Y
}

// mapPoints builds the points array mapping connection types for each coordinate
func mapPoints(lines []string) {
	pointsArray = make([]points, 0)

	for i, line := range lines {
		var ps = make([]point, 0)
		for j, r := range line {
			switch r {
			case '|':
				ps = append(ps, point{N: true, S: true, E: false, W: false}) // N,S
			case '-':
				ps = append(ps, point{N: false, S: false, E: true, W: true}) // E, W
			case 'L':
				ps = append(ps, point{N: true, S: false, E: true, W: false}) // N, E
			case 'J':
				ps = append(ps, point{N: true, S: false, E: false, W: true}) // N, W
			case '7':
				ps = append(ps, point{N: false, S: true, E: false, W: true}) // S, W
			case 'F':
				ps = append(ps, point{N: false, S: true, E: true, W: false}) // S, E
			case '.':
				ps = append(ps, point{N: false, S: false, E: false, W: false}) // ground
			case 'S':
				ps = append(ps, point{N: true, S: true, E: true, W: true}) // start
			default:
				log.Debug("ground point")
			}
			ps[j].identifier = r
			ps[j].coords.Y = i
			ps[j].coords.X = j
		}
		pointsArray = append(pointsArray, points{points: ps})
	}
}

// walk moves along the pipes storing poinst that mark loop locations
// it also keeps a track of last two moves
// returns the number of steps to traverse all pipes
func walk(tracker tracker) int {
	for ; tracker.steps == 0 || !comparePoints(tracker.init, tracker.point); tracker.steps++ {
		next := checkSouth(tracker.point)
		if !inLastMoves(tracker.last, next.coords) {
			log.Debug("moving south from ", string(tracker.point.identifier), " to ", string(next.identifier))
			tracker.point = next
			loop = append(loop, pointsArray[tracker.Y()].points[tracker.X()].coords)
			tracker.last = append(tracker.last[1:], next.coords)
			continue
		}
		next = checkEast(tracker.point)
		if !inLastMoves(tracker.last, next.coords) {
			log.Debug("moving east from ", string(tracker.point.identifier), " to ", string(next.identifier))
			tracker.point = next
			loop = append(loop, pointsArray[tracker.Y()].points[tracker.X()].coords)
			tracker.last = append(tracker.last[1:], next.coords)
			continue
		}
		next = checkNorth(tracker.point)
		if !inLastMoves(tracker.last, next.coords) {
			log.Debug("moving north from ", string(tracker.point.identifier), " to ", string(next.identifier))
			tracker.point = next
			loop = append(loop, pointsArray[tracker.Y()].points[tracker.X()].coords)
			tracker.last = append(tracker.last[1:], next.coords)
			continue
		}
		next = checkWest(tracker.point)
		if !inLastMoves(tracker.last, next.coords) {
			log.Debug("moving west from ", string(tracker.point.identifier), " to ", string(next.identifier))
			tracker.point = next
			loop = append(loop, pointsArray[tracker.Y()].points[tracker.X()].coords)
			tracker.last = append(tracker.last[1:], next.coords)
			continue
		}
		tracker.steps++ // the very last move will be back at start
	}
	return tracker.steps
}

// one returns the number of steps to reach the furthest point from the start
func one(lines []string) int {
	mapPoints(lines)

	tracker := newTracker()

	return walk(tracker) / 2
}