Check for poker straight - php

Question

I have managed to create an algorithm to check the rank of a poker hand. It works 100% correctly, but it's very slow. I've been analysing the code, and the check straight function is one of the slowest parts of it.
So my question is, is there a better way of calculating whether a hand make a straight?
Here is some details:
7 cards, 2 from holder, 5 from board. A can be high or low.
Each card is assigned a value:
2 = 2
3 = 3
..
9 = 9
T = 10
J = 11
Q = 12
K = 13
A = 14
The script has an array of all 7 cards:
$cards = array(12,5,6,7,4,11,3);
So now I need to be able to sort this into an array where it:
discards duplicates
orders the card from lowest to highest
only returns 5 consecutive cards I.e. (3,4,5,6,7)
It needs to be fast; loops and iterations are very costly. This is what I currently use and when it tries to analyse say 15000 hands, it takes its toll on the script.
For the above, I used:
discard duplicates (use array_unique)
order cards from lowest to highest (use sort())
only return 5 consecutive cards (use a for loop to check the values of cards)
Does anyone have any examples of how I could improve on this? Maybe even in another language that I could perhaps look at and see how it's done?

Answer 1

Instead of working with array deduping and sorting, consider using a bitmask instead, and setting bits to 1 where the card value is set. A bitmask works like a Set datastructure and comes with additional advantages when it comes to detecting contiguous elements.
for ($i = 0; $i < count($cards); $i++) {
$card = $cards[$i];
// For each card value, set the bit
if ($card == 14) {
// If card is an ace, also set bit 1 for wheel
$cardBitmask |= 0x2;
}
$cardBitmask |= (1 << $card);
}
// To compare, you simply write a for loop checking for 5 consecutive bits
for($i = 10; $i > 0; $i--)
{
if ($cardBitmask & (0x1F << $i) == (0x1F << $i)) {
// Straight $i high was found!
}
}

Answer 2

Consider the Java implementation at this link. I've included it here:
public static boolean isStraight( Card[] h )
{
int i, testRank;
if ( h.length != 5 )
return(false);
sortByRank(h); // Sort the poker hand by the rank of each card
/* ===========================
Check if hand has an Ace
=========================== */
if ( h[4].rank() == 14 )
{
/* =================================
Check straight using an Ace
================================= */
boolean a = h[0].rank() == 2 && h[1].rank() == 3 &&
h[2].rank() == 4 && h[3].rank() == 5 ;
boolean b = h[0].rank() == 10 && h[1].rank() == 11 &&
h[2].rank() == 12 && h[3].rank() == 13 ;
return ( a || b );
}
else
{
/* ===========================================
General case: check for increasing values
=========================================== */
testRank = h[0].rank() + 1;
for ( i = 1; i < 5; i++ )
{
if ( h[i].rank() != testRank )
return(false); // Straight failed...
testRank++; // Next card in hand
}
return(true); // Straight found !
}
}
A quick Google search for "check for poker straight (desired_lang)" will give you other implementations.

Answer 3

You could just sort the cards and loop over them in an array - saving always the last card and compare them with the current one.
$cards = array(12,5,6,7,4,11,3);
sort($cards);
$last = 0;
$count = 0;
$wheel = false;
foreach ($cards as $card) {
if ($card == $last) {
continue;
} else if ($card == ++$last) {
$count++;
} else {
if ($last == 6) $wheel = true;
$count = 1;
$last = $card;
}
if ($count == 5 || ($card == 14 && $wheel)) {
echo "straight $last";
$straight = range($last - 4, $last);
break;
}
}

Answer 4

You may go like this, you don't need to sort or anything (assuming that 2 is 2 and 14 is ace):
$cards = [12,5,6,7,4,11,3];
function _inc(&$i) {
if ($i == 14)
$i = 2;
else
$i++;
return $i;
}
$straight = false;
for($i = 2; $i <= 14; $i++) {
$ind = $i;
if (!in_array($ind, $cards)) continue;
$s = [$ind, _inc($ind), _inc($ind), _inc($ind), _inc($ind)];
$straight = count(array_intersect($s, $cards)) == count($s);
if ($straight) break;
}
print $straight;