9th day both parts

09/part1.php

@@ -0,0 +1,31 @@
+<?php
+
+$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+$input = array_map('str_split', $input);
+
+$sum       = 0;
+$lowpoints = 0;
+for ($i = 0; $i < count($input); $i++) {
+    for ($j = 0; $j < count($input[0]); $j++) {
+        $current = $input[$i][$j];
+
+        if (isset($input[$i - 1][$j]) && $input[$i - 1][$j] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i][$j - 1]) && $input[$i][$j - 1] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i][$j + 1]) && $input[$i][$j + 1] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i + 1][$j]) && $input[$i + 1][$j] <= $current) {
+            continue;
+        }
+        $sum += $current + 1;
+    }
+}
+
+echo $sum; //500

09/part2.php

@@ -0,0 +1,73 @@
+<?php
+
+$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+$input = array_map('str_split', $input);
+
+$sum = 0;
+$lowpoints = [];
+for ($i = 0; $i < count($input); $i++) {
+    for ($j = 0; $j < count($input[0]); $j++) {
+        $current = $input[$i][$j];
+
+        if (isset($input[$i - 1][$j]) && $input[$i - 1][$j] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i][$j - 1]) && $input[$i][$j - 1] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i][$j + 1]) && $input[$i][$j + 1] <= $current) {
+            continue;
+        }
+
+        if (isset($input[$i + 1][$j]) && $input[$i + 1][$j] <= $current) {
+            continue;
+        }
+        $sum += $current + 1;
+        $lowpoints[] = [$i + 1, $j + 1];
+    }
+}
+$basinSizes = [];
+
+$input = array_map(function ($line) {
+    array_unshift($line, 9);
+    array_push($line, 9);
+    return $line;
+}, $input);
+
+array_map(fn($line) => array_unshift($line, 9), $input);
+array_unshift($input, array_fill(0, count($input[0]), 9));
+$input[] = array_fill(0, count($input[0]), 9);
+
+foreach ($lowpoints as $lowpoint) {
+    $searched = [];
+    $input[$lowpoint[0]][$lowpoint[1]] = '*';
+    getBasinSize($input, $lowpoint[0], $lowpoint[1], $searched);
+    $basinSizes[] = count($searched);
+}
+
+function getBasinSize(&$input, $i, $j, &$searched)
+{
+    if (!isset($searched[$i . ',' . $j])) {
+        $searched[$i . ',' . $j] = 1;
+        if ($input[$i][$j] != '*') {
+            $input[$i][$j] = ' ';
+        }
+        if ($input[$i - 1][$j] != 9) {
+            getBasinSize($input, $i - 1, $j, $searched);
+        }
+        if ($input[$i][$j - 1] != 9) {
+            getBasinSize($input, $i, $j - 1, $searched);
+        }
+        if ($input[$i][$j + 1] != 9) {
+            getBasinSize($input, $i, $j + 1, $searched);
+        }
+        if ($input[$i + 1][$j] != 9) {
+            getBasinSize($input, $i + 1, $j, $searched);
+        }
+    }
+}
+
+rsort($basinSizes);
+echo array_product(array_slice($basinSizes, 0, 3)); //970200

README.md

@@ -37,5 +37,10 @@
 
 ### DAY 8 - Decoding 7-segments displays
 
+- [part1](08/part1.php)
+- [part2](08/part2.php)
+
+### DAY 9 - Smoke Basin
+
 - [part1](08/part1.php)
 - [part2](08/part2.php)