Need help-Strobogrammatical numbers

adrianpat · October 22, 2017

Hi,

I am a beginner in Php and I need your help for the following problem: I need to write a code to obtain the strobogrammatical numbers until 10000.

I start with the following code but I need your help for the final part:

<html>

<head>

<title>test upsideup </title>

</head>

<body>

<?php

function reverse_digit($digit){

switch($digit){

case 0:

return 0;

case 1:

return 1;

case 6:

return 9;

case 8:

return 8;

case 9:

return 6;

default:

return -1;

}

function testUSU($number){

$num2 = $number;

// current power of 10

$i = 0;

$reverse = 0;

while ($num2 > 0){

$i = $i + 1;

$num2 = $num2 / 10;

}

$reverse = $number % 10;

}

for ($x = 0; $x < 10; $x++) {

$num = reverse_digit($x);

if ($num != -1){

echo "digit = $x <br>";

echo "reverse = $num <br>\n";

}

//$test = 10.7;

//echo intval($test);

?>

</body>

</html>

Thanks,

Adrian

Barand · October 22, 2017

Here's my attempt

function is_strobo($n)
{
    $sdigits=[ '0' => '0',  '1' => '1',  '6' => '9',  '8' => '8', '9' => '6'  ];
    //      
    // reverse the digits
    //
    $ra = str_split("$n");
    $r = join('', array_reverse($ra));

    //
    // flip the digits
    //
    for ($i=0, $k=strlen($r); $i<$k; $i++)    {
        $d = $r[$i];
        if ( isset($sdigits[$d]) )    {
            $r[$i] = $sdigits[$d];
        } else  {
            return false;
        }
    }

    return $n==$r;                  // return true if it matches the original
}

Gandalf64 · October 23, 2017

Here's my version ->

<?php

function IsPrime($n) {
    for ($x = 2; $x < $n; $x++) {
        if ($n % $x == 0) {
            return 0;
        }
    }
    return 1;
}

function isStrob($num) {
    $myNumber = str_split($num);
    for ($i = 0; $i <= count($myNumber) / 2; $i++) {
        $c = $myNumber[$i];
        $b = $myNumber[count($myNumber) - 1 - $i];
        if (!isValid($c, $b)) {
            return FALSE;
        }
    }
    return TRUE;
}

function isValid ($c, $b) {
    switch ($c) {
        case '1':
            return $b == '1';
        case '6':
            return $b == '9';
        case '9':
            return $b == '6';
        case '8':
            return $b == '8';
        case '0':
            return $b == '0';
        default:
            return FALSE;
    }
}


function get_strobogrammatic_numbers($total = 10000) {
    for ($i = 0; $i <= $total; $i++) {
        $status = isStrob($i);
        if ($status) {
            $strob_numbers[] = $i;
        }
    }
    return $strob_numbers;
}

$result = get_strobogrammatic_numbers(1000);

//echo "<pre>" . print_r($result, 1) . "</pre>";
?>

<!DOCTYPE html>
<html lang="en">
    <head>
        <title>Test Upside Up</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
    </head>
    <body>
        <div>Strobogrammatic Numbers</div>
        <?php
        echo "<p>";
        for ($x = 0; $x < count($result); $x++) {
            if ($x === count($result) - 1) {
                echo $result[$x] . ".<p>";
            } else {
                echo $result[$x] . ", ";
            }
        }
        ?>
    </body>
</html>

Barand · October 23, 2017

FYI, when checking if prime, your for loop only needs to check as far as sqrt(n).

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