Gray code to binary conversion

Given a gray code f开发者_运维知识库or a number, find the binary code for the number.

Gray code is a binary numeral system where two successive values differ in only one bit.

For Example two bit gray code is: 0 - 00 1 - 01 2 - 11 3 - 10

Binary is:

0 - 00 1 - 01 2 - 10 3 - 11

Provide an algorithm to convert the gray code of the number to binary code.

For example, input is 11. Expected output is 10.

Converting the Gray code to binary is:

Retain the Most significant bit as it is and for the rest of the bits keep xoring the successive bits.

ie Gn Gn-1 Gn-2 ........ G1 is the gray code and Bn Bn-1 .......B1 is the binary code.

Bn= Gn and for all the other bits Bn-1 = Gn-1 XOR Gn

If you want an easy way there is a good online gray code converter that you can use: http://www.convertforfree.com/gray-code-converter/

<?php

function gry_code($n) {

if($n == 0 || $n > 65 ) {

    return "Invalid input please input between 1 to 65";
    exit;

} 

$arr = array();

array_push($arr,"0","1");

$i = 0;
$j = 0;

 for ($i = 2; $i < (1<<$n); $i = $i<<1)
 {
    //duplicate the arr contents in reverse order
    for ($j = $i-1 ; $j >= 0 ; $j--)

    array_push($arr,$arr[$j]);

    // append 0 to the first half
    for ($j = 0 ; $j < $i ; $j++)
        $arr[$j] = "0".$arr[$j];

    // append 1 to the second half
    for ($j = $i ; $j < 2*$i ; $j++)
        $arr[$j] = "1".$arr[$j];
}
//return $arr;
$arr = array_slice($arr, -$n);
foreach($arr as $key => $arrx) {

    echo $arrx."\n";


}

//return $arr;

}

print_r(gry_code(5));

?>