first commit - working

vendor/sebastian/diff/src/MemoryEfficientLongestCommonSubsequenceCalculator.php

@@ -0,0 +1,88 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/diff.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Diff;
+
+use function array_fill;
+use function array_merge;
+use function array_reverse;
+use function array_slice;
+use function count;
+use function in_array;
+use function max;
+
+final class MemoryEfficientLongestCommonSubsequenceCalculator implements LongestCommonSubsequenceCalculator
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function calculate(array $from, array $to): array
+    {
+        $cFrom = count($from);
+        $cTo   = count($to);
+
+        if ($cFrom === 0) {
+            return [];
+        }
+
+        if ($cFrom === 1) {
+            if (in_array($from[0], $to, true)) {
+                return [$from[0]];
+            }
+
+            return [];
+        }
+
+        $i         = (int) ($cFrom / 2);
+        $fromStart = array_slice($from, 0, $i);
+        $fromEnd   = array_slice($from, $i);
+        $llB       = $this->length($fromStart, $to);
+        $llE       = $this->length(array_reverse($fromEnd), array_reverse($to));
+        $jMax      = 0;
+        $max       = 0;
+
+        for ($j = 0; $j <= $cTo; $j++) {
+            $m = $llB[$j] + $llE[$cTo - $j];
+
+            if ($m >= $max) {
+                $max  = $m;
+                $jMax = $j;
+            }
+        }
+
+        $toStart = array_slice($to, 0, $jMax);
+        $toEnd   = array_slice($to, $jMax);
+
+        return array_merge(
+            $this->calculate($fromStart, $toStart),
+            $this->calculate($fromEnd, $toEnd)
+        );
+    }
+
+    private function length(array $from, array $to): array
+    {
+        $current = array_fill(0, count($to) + 1, 0);
+        $cFrom   = count($from);
+        $cTo     = count($to);
+
+        for ($i = 0; $i < $cFrom; $i++) {
+            $prev = $current;
+
+            for ($j = 0; $j < $cTo; $j++) {
+                if ($from[$i] === $to[$j]) {
+                    $current[$j + 1] = $prev[$j] + 1;
+                } else {
+                    $current[$j + 1] = max($current[$j], $prev[$j + 1]);
+                }
+            }
+        }
+
+        return $current;
+    }
+}