CODEWITHSUNDEEP
php
Viacom
Viacom

Reputation: 11

PHP likely chance

Okay, so i don't really know how I go about this.

I'm currently working on a lottery system for a game.

I have a table with virtual items which I want to randomly select by a likely chance.

Table examples: 

ID = 1, item_name = Sword, likely_chance = 75  
ID = 2, Item_name = 10,000, likely_chance = 20

For id 2, 10,000 represents 10,000 coins.

I want to come up with an algorithm which will select a item with a higher chance of selecting a higher likely chance but also still be able to win a item with a lower likely chance rarely.

Upvotes: 0

Views: 123

Answers (1)

Yeldar Kurmangaliyev
Yeldar Kurmangaliyev

Reputation: 34234

If you have items with "likely chances" of C1, C2, C3...Cn, then you can calculate the sum Ctotal.

Then, you can get a random value between 0 and Ctotal, and walk through your array (order is irrelevant) until the sum of "skipped" items exceeds this random value.

For example, in your case, Ctotal = 75 + 20 = 95. Get a random number between 0 and 95, and if it is less than 75 - give a sword; else - give 10000 coins. It will provide a fair winnings distribution according to your likely chances - 78.95% and 21.05%, respectively.

$items = ['Sword', '10000 coins'];
$chances = [70, 25];

$ctotal = array_sum($chances); echo "Total is $ctotal\n";
$rand = rand(0, $ctotal); echo "Rand is $rand\n";

$i = 0;
$currentSum = 0;
while (true)
{
    $currentSum += $chances[$i];
    if ($currentSum >= $rand)
    {
        echo "You win: ".$items[$i];
        break;
    }
    $i++;
}

Here is the working Demo. Note that IDEOne remembers the last output and doesn't run this program again every time. The output will appear to be the same, but it is not.

Upvotes: 1

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