compiler/examples/fannkuchredux.php

<?php
/* The Computer Language Benchmarks Game
  https://salsa.debian.org/benchmarksgame-team/benchmarksgame/

  Naive transliteration from Rex Kerr's Scala program
  contributed by Isaac Gouy
*/

function fannkuch($n)
{
    $perm1 = [];
    for ($i = 0; $i < $n; $i++) $perm1[$i] = $i;
    $perm = [];
    $count = [];
    $f = $flips = $nperm = $checksum = $i = $k = $r = 0;

    $r = $n;
    while ($r > 0) {
        $i = 0;
        while ($r != 1) {
            $count[$r - 1] = $r;
            $r -= 1;
        }

        while ($i < $n) {
            $perm[$i] = $perm1[$i];
            $i += 1;
        }

        // Count flips and update max and checksum
        $f = 0;
        $k = $perm[0];

        while ($k != 0) {
            $i = 0;
            while (2 * $i < $k) {
                $t = $perm[$i];
                $perm[$i] = $perm[$k - $i];
                $perm[$k - $i] = $t;
                $i += 1;
            }
            $k = $perm[0];
            $f += 1;

        }

        if ($f > $flips) $flips = $f;
        if (($nperm & 0x1) == 0) $checksum += $f; else $checksum -= $f;

        // Use incremental change to generate another permutation
        $more = true;
        while ($more) {
            if ($r == $n) {
                echo $checksum, "\n";
                return $flips;
            }
            $p0 = $perm1[0];
            $i = 0;
            while ($i < $r) {
                $j = $i + 1;
                $perm1[$i] = $perm1[$j];
                $i = $j;
            }
            $perm1[$r] = $p0;

            $count[$r] -= 1;
            if ($count[$r] > 0) $more = false; else $r += 1;
        }
        $nperm += 1;
    }
    return $flips;
}

function main()
{
    global $argc, $argv;
    $n = $argc > 2 ? $argv[2] : 7;
    $begin = microtime(true);
    printf("Pfannkuchen(%d) = %d\n", $n, fannkuch($n));
    echo "Time: ", microtime(true) - $begin, "\n";
}