Daily Challenge #77 - Bird Mountain

const starPattern = [[0, 0], [-1, 0], [1, 0], [0, -1], [0, 1]];

const hillCount = (mountains: string[][]): number =>
  mountains.reduce((acc, row) => acc + row.reduce((acc, dot) => acc + Number(dot === "^"), 0), 0);

const peakHeight = (mountains: string[][]): number =>
  Array.from({
    length: mountains.length,
  }).findIndex(() => {
    if (hillCount(mountains) === 0) return true;
    mountains = mountains.map((row, rowIndex) =>
      row.map((_, colIndex) =>
        starPattern.reduce((acc, [x, y]) => acc && (mountains[rowIndex + y] || [])[colIndex + x] == "^", true)
          ? "^"
          : " "
      )
    );
    return false;
  });

const mountains = [
      "^^^^^^        ".split(''),
      " ^^^^^^^^     ".split(''),
      "  ^^^^^^^     ".split(''),
      "  ^^^^^       ".split(''),
      "  ^^^^^^^^^^^ ".split(''),
      "  ^^^^^^      ".split(''),
      "  ^^^^        ".split('')
    ]

;; These could be improved into a macro but want readability
(defn check-left [row col mountains]
  "Checks the cell to the left"
  (if (and (>= (- col 1) 0) 
           (.equals ((mountains row) (- col 1)) "^"))
    true
    false))
(defn check-up [row col mountains]
  "Checks the cell above"
  (if (and (>= (- row 1) 0) 
           (.equals ((mountains (- row 1)) col) "^"))
    true
    false))
(defn check-right [row col mountains]
  "Checks the cell to the right"
  (if (and (< (+ col 1) (count (mountains row))) 
           (.equals ((mountains row) (+ col 1)) "^"))
    true
    false))
(defn check-down [row col mountains]
  "Checks the cell below"
  (if (and (< (+ row 1) (count mountains)) 
           (.equals ((mountains (+ row 1)) col) "^"))
    true
    false))

(defn will-erode? [row col mountains]
  "Returns true if the current cell is not completely surrounded by mountains"
  (not 
   (and (check-left row col mountains)
        (check-up row col mountains)
        (check-right row col mountains)
        (check-down row col mountains))))

(defn erode-mountains [mountains errosion-symbol]
  "Erodes the mountains once"
  (into [] 
        (map-indexed
         (fn [row-index row]
           (into [] 
                 (map-indexed
                  (fn [col-index col]
                    (if (and (.equals col "^")
                             (will-erode? row-index col-index mountains))
                      errosion-symbol
                      col))
                  row)))
         mountains)))

(defn fully-eroded? [mountains]
  (nil? 
    (first (filter #(.equals "^" %)
                   (flatten mountains)))))

(defn peak-height [mountains]
  "Get the peak height (according to a fictional bird)"
  (loop [times 0
         mts mountains]
    (if-not (fully-eroded? mts)
        (recur (+ times 1) (erode-mountains mts times))
    times)))

(def mountains [
  [ "^" "^" "^" "^" "^" "^" " " " " " " " " " " " " " " " " ]
  [ " " "^" "^" "^" "^" "^" "^" "^" "^" " " " " " " " " " " ]
  [ " " " " "^" "^" "^" "^" "^" "^" "^" " " " " " " " " " " ]
  [ " " " " "^" "^" "^" "^" "^" " " " " " " " " " " " " " " ]
  [ " " " " "^" "^" "^" "^" "^" "^" "^" "^" "^" "^" "^" " " ]
  [ " " " " "^" "^" "^" "^" "^" "^" " " " " " " " " " " " " ]
  [ " " " " "^" "^" "^" "^" " " " " " " " " " " " " " " " " ]
])

(peak-height mountains)
;; 3

#!/usr/bin/perl
use warnings;
use strict;

use List::Util qw{ max };

sub populate {
    my ($view) = @_;
    my @grid;
    my $y = 1;
    my $max_x = 0;
    for my $line (split /\n/, $view) {
        my $x = 0;
        for my $char (split //, " $line") {
            $grid[$y][$x++] = (0, undef)[$char eq ' '];
            $max_x = $x if $x > $max_x;
        }
        ++$y;
    }
    return $max_x, @grid, []
}

sub height {
    my ($view) = @_;
    my ($max_x, @grid) = populate($view);
    my @height = map [ map defined $_ ? 0 : -1, @{ $grid[$_] }[0 .. $max_x] ],
                 0 .. $#grid;
    my $max_height = 0;
    my $change = 1;
    while ($change) {
        undef $change;
        show(@height);
        my @next = map [ @$_ ], @height;
        for my $x (0 .. $max_x) {
            for my $y (0 .. $#grid) {
                my @neighbours
                    = map $height[ $_->[1] ][ $_->[0] ] // -1,
                      grep $_->[1] >= 0 && $_->[0] >= 0,
                      [$x-1, $y], [$x+1, $y], [$x, $y-1], [$x, $y+1];
                if ($height[$y][$x] == 0
                    && grep $_ == $max_height - 1, @neighbours
                ) {
                    $next[$y][$x] = 1 + max(@neighbours);
                    $change = 1;
                }
            }
        }
        @height = @next;
        ++$max_height unless $max_height;
        ++$max_height;
    }
    return $max_height - 2
}

sub show {
    for my $line (@_) {
        printf '%3s', $_ for @$line;
        print "\n";
    }
    print "\n";
}

use Test::More tests => 4;

is height(<< '__INPUT__'), 2;
^^^
^^^
^^^
__INPUT__

is height(<< '__INPUT__'), 2;
^^^^^^^
^^^^^^^
^^^^^^^
^^^ ^^^
^^^^^^^
^^^^^^^
^^^^^^^
__INPUT__

is height(<< '__INPUT__'), 4;
^^^^^^^
^^^^^^^
^^^^^^^
^^^^^^^
^^^^^^^
^^^^^^^
^^^^^^^
__INPUT__

is height(<< '__INPUT__'), 3;
^^^^^^
 ^^^^^^^^
  ^^^^^^^
  ^^^^^
  ^^^^^^^^^^^^^
  ^^^^^^
  ^^^^
__INPUT__