Problem ProjectEuler 044

ProjectEuler/044/solve.php

@@ -0,0 +1,32 @@
+<?php
+
+function Pn($n)
+{
+    return $n * (3 * $n - 1) / 2;
+}
+
+$pn = [];
+for ($i = 1; $i < 2500; $i++) {
+    $pn[] = (int) Pn($i);
+}
+$smallest_diff = PHP_INT_MAX;
+echo "Precalculate done\n";
+for ($ij = 0; $ij < sizeof($pn); $ij++) {
+    echo "$ij%\n";
+    $j = $pn[$ij];
+    for ($ik = $ij + 1; $ik < sizeof($pn); $ik++) {
+        $k = $pn[$ik];
+        $sum = $j + $k;
+        if (in_array($sum, $pn)) {
+            $diff = (int) abs($k - $j);
+            if (in_array($diff, $pn, true)) {
+                if ($diff < $smallest_diff) {
+                    $smallest_diff = $diff;
+                    echo "Found: Pn($ij)=$j Pn($ik)=$k Sum: $sum Diff: $diff\n";
+                }
+            }
+        }
+    }
+}
+
+echo "Smallest diff: $smallest_diff";