This is a very basic algorithm for a "magic trick" where you choose the same letter 3 times (in your mind) from a set of different letters distributed in 3 columns and the system will guess which one you choose.

magicTrick.php

<?php

    $letters = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U'];
    
    shuffle($letters);
    $count = 1;   
    $message = "";
    
    do {
    
        printLetters($letters);
        echo "\n";
        
        if ($count === 1) {
            $message = "Select one letter (in your mind) and type the column number where it is (1,2,3): ";
        } elseif ($count === 2) {
            $message = "Look for the same letter and type the column number where it is now (1,2,3): ";
        } else {
            $message = "Look for the same letter again (last time, I promise) and type the column number where it is now (1,2,3): ";
        }
        
        echo $message;
        $input = fopen ("php://stdin","r");
        $value = (int)fgets($input) -1;
        
        while (!valid($value)) {
            echo "Please enter a valid colum number (1,2,3): ";
            $input = fopen ("php://stdin","r");
            $value = (int)fgets($input) -1;
            echo "\n";
        }
        
        echo "\n";
        
        $letters = reArrange($letters, $value);    
        $count++;
        
    } while ($count <= 3);
    
    echo "\n";
    echo "\n";
    echo "\n*** The letter you choose is: $letters[10] ***\n\n";
  
//Display in a 'pretty' format the letters in 3 columns   
function printLetters(array $arrayLetters) 
{
    echo "\tColum 1\t\tColum 2\t\tColum 3\n";
    echo "-------------------------------------------------\n";
    for ($i = 0; $i < count($arrayLetters); $i++) {
    
        echo "\t   ".$arrayLetters[$i]."\t";
        
        if (($i+1) % 3 === 0) {
            echo "\n";
        }
    }
}

/* 
   Arrange the cards, in order to the 'trick' works,
   the column picked by the user should be moved to
   the middle (always)
*/
function reArrange(array $arrayToArrange, $index)
{
    $reArranged = array();
    $cols = array();
        
    for($i = 0; $i < 7; $i++) {
        for ($j = 0; $j < 3; $j++) {
            $cols[$j][$i] = array_shift($arrayToArrange);
        }
    }
    
    $reArranged[1] = $cols[$index];
    unset($cols[$index]);
    $reArranged[0] = array_shift($cols);
    $reArranged[2] = array_shift($cols);  
    
    return array_merge($reArranged[0], $reArranged[1], $reArranged[2]);
}

//Validate if the value the user typed is a number and in a valid range
function valid($value)
{
   if (!in_array($value, array(0,1,2), true)) {
       return false;
   }   
    return true;
}