aoc2019/day-3/src/main.kt

package main

import java.io.File
import kotlin.math.abs
import kotlin.math.max
import kotlin.math.min

fun main() {
    val coll = loadLines(File("./input").readText())

    val intersections = coll.intersections();
    // Get shorted manhattan path
    println("Shortest manhattan distance: ")
    println(intersections.map { abs(it.x) + abs(it.y) }.sorted().first())
    println("Shortest wire distance: ")
    println(intersections.map { it.segmentA.getDistance(it) + it.segmentB.getDistance(it) }.sorted().first())
}

/**
 * Really dirty line reader that makes a LineCollection from input
 */
fun loadLines(input: String): LineCollection {
    return LineCollection(
      input
        .trim()
        // Split lines
        .lines()
        .map {
            // This records the current point in the line
            var current = Point(0, 0)
            Line(
              it
                .trim()
                // Segments are split with ,
                .split(',')
                .map {
                    // First character is the direction
                    var d = it[0];
                    // Rest is distance/length
                    var distance = it.substring(1).toInt()

                    // Down and Left are basically Up and Right but inverted.
                    if (d == 'D' || d == 'L') {
                        d = if (d == 'D') 'U' else 'R'
                        distance = -distance
                    }

                    if (d == 'U') {
                        // if direction is up, line is over the Y axis
                        Segment(Axis.Y, current.y, current.y + distance, current.x).also {
                            // Set the new current point
                            current = Point(current.x, current.y + distance);
                        }
                    } else {
                        // If direction is anything else it's Right, so it runs over the X axis
                        Segment(Axis.X, current.x, current.x + distance, current.y).also {
                            // Set the new current point
                            current = Point(current.x + distance, current.y);
                        }
                    }
                }
            )
        }
    )
}

// Helper class indicating a point (x, y) coordinates
data class Point(val x: Int, val y: Int)

// Class that holds all lines known
data class LineCollection(val lines: List<Line>) {
    fun intersections(): List<Intersection> {
        val items = mutableListOf<Intersection>()
        for (i in 0 until lines.count() - 1) {
            for (j in (i + 1) until lines.count()) {
                items.addAll(lines[i].intersections(lines[j]));
            }
        }

        return items;
    }
}

// Helper class that holds a segment and it's corresponding line
data class LineSegment(val line: Line, val segment: Segment) {
    // Get distance to point in line.
    // It is assumed that the point is part of the [segment]
    fun getDistance(it: Point): Int {
        // Since point intersects, use the point coordinate instead of [Segment.end]
        val lastEnd = if (segment.axis == Axis.X) it.y else it.x
        // Distance traveled
        var cost = 0
        for (sgm in line.segments) {
            // If we found the same segment as we're holding we can stop
            if (sgm === segment) {
                break
            }

            // Add length of segment to cost
            cost += sgm.high - sgm.low
        }

        // Get length to point from last segment start
        return cost + (max(lastEnd, segment.start) - min(lastEnd, segment.start))
    }

    fun getDistance(it: Intersection) = getDistance(Point(it.x, it.y))
}

// Holds an intersection, it's point and the 2 LineSegments intersecting
data class Intersection(val x: Int, val y: Int, val segmentA: LineSegment, val segmentB: LineSegment)

// Line is a collection of Segments
data class Line(val segments: List<Segment>) {
    // Find all intersections between this and given line
    fun intersections(rhs: Line): List<Intersection> {
        // flatMap will allow use to return an array
        // and will concat all returned arrays
        return segments.flatMap { seg ->
            // map but it ignores all null returns
            rhs.segments.mapNotNull { otherSeg ->
                // Find intersection ( ?. indicates only access .let if result is not null )
                otherSeg.intersection(seg)?.let {
                    // Create intersection object
                    Intersection(it.x, it.y, LineSegment(this, seg), LineSegment(rhs, otherSeg))
                }
            }
        }
    }
}

// Quick helper function to make a range between 2 ints
infix fun Int.between(rhs: Int) = (this + 1) until rhs

// Enum with known Axis'es
enum class Axis {
    X,
    Y;
}

// Class for a segment in a line, a segment is basically a single direction stroke
//
// if [axis] is X, [start] and [end] are on the X axis, and [other] is on the Y axis
// if [axis] is Y, [start] and [end] are on the Y axis, and [other] is on the X axis
data class Segment(val axis: Axis, val start: Int, val end: Int, val other: Int) {
    // Get the lowest value from start or end
    // helpful for intersection calculation
    val low by lazy { min(start, end) }

    // Get the highest value from start or end
    // helpful for intersection calculation
    val high by lazy { max(start, end) }

    // Find intersection between 2 segments
    fun intersection(rhs: Segment): Point? {
        // If 2 lines are on a different axis,
        // the calculations are different from them being on the same axis
        return if (axis != rhs.axis) {
            // If on different axis, check if [other] is between each others [low] and [high]
            if (rhs.other in low between high && other in rhs.low between rhs.high) {
                if (rhs.axis == Axis.Y) {
                    Point(other, rhs.other)
                } else {
                    Point(rhs.other, other)
                }
            } else {
                null
            }
        } else {
            // If lines are on the same axis, [which is an edge case that never happens :)]
            // [other] should be the same for both to intersect
            if (other != rhs.other) {
                null
            } else {
                // only intersect if our [high] is higher than their [low] and vice versa
                if (low < rhs.high && rhs.low < high) {
                    val first = min(rhs.high, high)
                    Point(if (axis == Axis.Y) other else first, if (axis == Axis.Y) first else other)
                } else {
                    null
                }
            }
        }
    }
}