Add PHP example for chapter 09 - dynamic programming (#98)

09_dynamic_programming/php/01_longest_common_subsequence.php

@@ -0,0 +1,45 @@
+<?php
+
+/**
+ * @param string $stringA
+ * @param string $stringB
+ * @return array
+ */
+function search(string $stringA, string $stringB): array
+{
+    $cell = [];
+
+    for ($i = 0; $i < strlen($stringA); $i++) {
+        for ($j = 0; $j < strlen($stringB); $j++) {
+            if ($stringA[$i] === $stringB[$j]) {
+                if (isset($cell[$i - 1][$j - 1])) {
+                    $cell[$i][$j] = $cell[$i - 1][$j - 1] + 1;
+                } else {
+                    $cell[$i][$j] = 1;
+                }
+            } else {
+                if (isset($cell[$i - 1][$j]) || isset($cell[$i][$j - 1])) {
+                    $cell[$i][$j] = max(
+                        isset($cell[$i - 1][$j]) ? $cell[$i - 1][$j] : 0,
+                        isset($cell[$i][$j - 1]) ? $cell[$i][$j - 1] : 0
+                    );
+                } else {
+                    $cell[$i][$j] = 0;
+                }
+            }
+        }
+    }
+
+    return $cell;
+}
+
+print_r(search('fish', 'fosh'));
+
+/*
+[      f o s h
+    f [1,1,1,1],
+    i [1,1,1,1],
+    s [1,1,2,2],
+    h [1,1,2,3]
+]
+*/