Advent of Code 2021-15.scala

import java.io.FileInputStream
import scala.annotation.tailrec
import scala.io.StdIn

case class Point(x: Int, y: Int):
  def add(dx: Int, dy: Int): Point =
    Point(x + dx, y + dy)

case class Link(point: Point, cost: Int)

@tailrec
def _findMinimumPath(riskMap: Vector[Vector[Int]], visited: Set[Point], nexts: Vector[Link], dest: Point): Int =
  val current = nexts.head
  val point = current.point
  if point == dest then
    val cost = current.cost + riskMap(point.y)(point.x)
    cost
  else if visited.contains(point) then
    _findMinimumPath(riskMap, visited, nexts.tail, dest)
  else if 0 > point.x || 0 > point.y || riskMap.size <= point.y || riskMap(0).size <= point.x then
    _findMinimumPath(riskMap, visited, nexts.tail, dest)
  else
    val cost = current.cost + riskMap(point.y)(point.x)
    val nextVisited = visited + point
    val availables = Vector(
      Link(point.add(1, 0), cost),
      Link(point.add(0, 1), cost),
      Link(point.add(-1, 0), cost),
      Link(point.add(0, -1), cost)
    )
    _findMinimumPath(riskMap, nextVisited, (nexts.tail ++ availables).sortBy(_.cost), dest)


val nexts = Vector(
  Link(Point(1, 0), 0),
  Link(Point(0, 1), 0),
)

def solve15_1(inputs: Vector[Vector[Int]]): Int =
  _findMinimumPath(inputs, Set(Point(0, 0)), nexts, Point(inputs(0).size - 1, inputs.size - 1))

def solve15_2(inputs: Vector[Vector[Int]]): Int =
  val width = inputs(0).size
  val height = inputs.size
  val riskMap: Vector[Vector[Int]] =
    (0 until height * 5).map { y =>
      (0 until width * 5).map { x =>
        val risk = inputs(y % height)(x % width) + (y / height) + (x / width)
        (risk - 1) % 9 + 1
      }.toVector
    }.toVector

  _findMinimumPath(riskMap, Set(Point(0, 0)), nexts, Point(riskMap(0).size - 1, riskMap.size - 1))

@main def solve15(): Unit =
  val in = new FileInputStream("example15-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .map(line => line.map(_.toInt - '0').toVector)
    .toVector
  println(solve15_1(inputs))
  println(solve15_2(inputs))