day3.php

<?php

function readInput()
{
    $wires = [];

    if ($file = fopen("input/day3.txt", "r")) {
        while ($line = fgets($file)) {
            $wires[] = explode(",", $line);
        }
        fclose($file);
    }

    return $wires;
}

function plotGrid($wires)
{
    $grid = [];
    $wireLength = [];
    $wireID = 0;

    foreach ($wires as $w) {
        $posX = 0;
        $posY = 0;
        $wl = 0;
        $wireLength[$wireID][$posX][$posY] = $wl;

        foreach ($w as $ins) {
            $direction = str_split($ins)[0];
            $length = trim(substr($ins, 1));

            switch ($direction) {
                case 'U':
                    for ($i = $posY; $posY < $i + $length;) {
                        $grid[$posX][++$posY][] = $wireID;
                        $wl++;
                        //echo "U - id $wireID X $posX Y $posY L $wl\n";
                        $wireLength[$wireID][$posX][$posY] = $wl;
                    }
                    break;
                Case 'D':
                    for ($i = $posY; $posY > $i - $length;) {
                        $grid[$posX][--$posY][] = $wireID;
                        $wl++;
                        $wireLength[$wireID][$posX][$posY] = $wl;
                    }
                    break;
                Case 'L':
                    for ($i = $posX; $posX > $i - $length;) {
                        $grid[--$posX][$posY][] = $wireID;
                        $wl++;
                        $wireLength[$wireID][$posX][$posY] = $wl;
                    }
                    break;
                Case 'R':
                    for ($i = $posX; $posX < $i + $length;) {
                        $grid[++$posX][$posY][] = $wireID;
                        $wl++;
                        //echo "R - id $wireID X $posX Y $posY L $wl\n";
                        $wireLength[$wireID][$posX][$posY] = $wl;
                    }
                    break;
            }
        }

        $wireID++;
    }

    //print_r($wireLength);

    return [$grid, $wireLength];
}


function part1()
{
    $wires = readInput();

    $grid = plotGrid($wires)[0];

    $mdClosestToPort = null;

    foreach ($grid as $X => $arrY) {
        foreach ($arrY as $Y => $wireIDs) {
            // Find intersection
            if (count($wireIDs) > 1) {

                // Calculate Manhattan distance
                if ($X < 0) {
                    $X = -$X;
                }
                if ($Y < 0) {
                    $Y = -$Y;
                }
                $i = $X + $Y;

                if ($i < $mdClosestToPort && $i != 0 || $mdClosestToPort == null) {
                    $mdClosestToPort = $i;
                }
            }
        }
    }

    return $mdClosestToPort;
}


function part2()
{
    $wires = readInput();
    //$wires = [["U7", "R4"], ["R2", "U3", "L4"]];
    //$wires = [["R2", "U3"]];
    //$wires = [["U3", "R3", "D3", "L3"]];


    /*

    |
    |
    |
    |
  --+-|
    | |
    | |
     --

    */

    $grid = plotGrid($wires);
    $wireLength = $grid[1];

    //print_r($wireLength);

    $lClosestToPort = null;

    foreach ($grid[0] as $X => $arrY) {
        foreach ($arrY as $Y => $wireIDs) {
            // Find intersection
            if (count($wireIDs) > 1) {
                // Calculate wirelength from this point.
                $lengthFromO1 = $wireLength[$wireIDs[0]][$X][$Y];
                $lengthFromO2 = $wireLength[$wireIDs[1]][$X][$Y];
                $totalLength = $lengthFromO1 + $lengthFromO2;

                if ($totalLength < $lClosestToPort || $lClosestToPort == null) {
                    echo "WireID 0: {$wireIDs[0]} WireID 1: {$wireIDs[1]}\n";
                    echo "Line1 Length: $lengthFromO1 Line2 Length: $lengthFromO2 Total $totalLength\n";
                    echo "X: $X Y: $Y\n";
                    $lClosestToPort = $totalLength;
                }
            }
        }
    }

    return $lClosestToPort;
}

echo "Part 1 " . part1() . "\n";
echo "Part 2 " . part2() . "\n";