<?php
 
// Length of a randomly generated String
$string_length = 9;	
 
// Number of strings that will be generated
$tries = 3000000;
 
// Arbitrary pool of characters
// These will be used to generate the string
$character_pool = '1234567890abcdefghijklmnopqrstuvwxyz';
$pool_size      = strlen($character_pool);
 
// Maximum number of combinations
// Given the length of strings and available characters
$combination_count = pow($pool_size, $string_length);
 
echo "With a character pool of $pool_size characters you can generate $combination_count unique strings of $string_length characters long.\n";
 
/**
 * Secondary Consideration
 * 
 * The probability of any one of a number of generations ($tries) matching a
 * previously generated value.
 * 
 * This only returns 100%, am I missing something?
 */
 
$probability = pow(1 - 1/$combination_count, $tries);
 
echo "The probabiity of generating a match with a previously generated string after $tries tries is ".round($probability*100,2)."%.\n";

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