From f5ef44c5be4ea6d4e3137014aa5788236eab4b6d Mon Sep 17 00:00:00 2001
From: Lubos Kolouch <lubos@kolouch.net>
Date: Sat, 26 Feb 2022 13:11:09 +0100
Subject: feat(lubos-kolouch/php/ch-1.php): Challenge 153 Task 1 PHP LK

---
 challenge-153/lubos-kolouch/php/ch-1.php | 59 ++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 challenge-153/lubos-kolouch/php/ch-1.php

diff --git a/challenge-153/lubos-kolouch/php/ch-1.php b/challenge-153/lubos-kolouch/php/ch-1.php
new file mode 100644
index 0000000000..7b7c50e199
--- /dev/null
+++ b/challenge-153/lubos-kolouch/php/ch-1.php
@@ -0,0 +1,59 @@
+<?php
+
+class LeftFactCalculator {
+
+    public function __construct() {
+        # keep seen factorials in a cache to speed things up
+        $this->fact_cache = [0 => 1];
+        $this->left_fact_cache = [0 => 0];
+    }
+
+    public function calculate_factorial(int $what) {
+
+        if (array_key_exists($what, $this->fact_cache)) {
+            return $this->fact_cache[$what];
+        }
+
+        # let's utilize the fact that we are processing the numbers in sequence
+        $this->fact_cache[$what] = $what * $this->fact_cache[$what - 1];
+
+        return $this->fact_cache[$what];
+    }
+
+    public function calculate_left_fact(int $what) {
+
+        if (array_key_exists($what, $this->left_fact_cache)) {
+            return $this->left_fact_cache[$what];
+        }
+
+        # let's utilize the fact that we are processing the numbers in sequence
+        $this->left_fact_cache[$what] = $this->calculate_factorial($what - 1) + $this->left_fact_cache[$what - 1];
+
+        return $this->left_fact_cache[$what];
+    }
+
+    public function get_left_factorial(int $what) {
+
+        $output = [];
+
+        foreach (range(1, $what) as $i) {
+            $output[] =  $this->calculate_left_fact($i);
+        }
+
+        return $output;
+    }
+}
+
+$calculator = new LeftFactCalculator();
+array_diff($calculator->get_left_factorial(10), [
+        1,
+        2,
+        4,
+        10,
+        34,
+        154,
+        874,
+        5914,
+        46234,
+        409114,
+    ]) == [] or throw new Exception("Failed test 1");
-- 
cgit