PHP Left rotate array in PHP

Question

I am trying to left rotate an array in PHP 2 times. It works correctly but there is a blank space in the array from some unknown reason. This is my code:

$a_temp = fgets($handle);
$a = explode(" ",$a_temp);
for($i = 0; $i < 2; $i++){
    print_r($a);
    array_unshift($a, array_pop($a));
    print_r($a);
}

The file has something like this:

1 2 3

Now the output I get is:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3

)
Array
(
    [0] => 3

    [1] => 1
    [2] => 2
)
Array
(
    [0] => 3

    [1] => 1
    [2] => 2
)
Array
(
    [0] => 2
    [1] => 3

    [2] => 1
)

As you can see, every time a rotate is performed, it introduces a blank space in it and during printing the array, it appears as a new line character. Any ideas what I am doing wrong?

Make sure your element is "3" and not, say, "3\n". (Notice how the first print_r has that extra space too, right before the closing paren. That hints the problem is in the input.) — cHao
– cHao, Commented Jan 26, 2017 at 15:11
I ran your code here and it worked fine. But I started with $a = [1, 2, 3];. Don't know what you started with because you did not include it in your question — inorganik
– inorganik, Commented Jan 26, 2017 at 15:12
Ran your code with $a = array(1,2,3); look fine with me no new lines. — haiderktk
– haiderktk, Commented Jan 26, 2017 at 15:14
Check it out yourself : eval.in/724856 works fine. Make sure you've got no stray newlines in your array. — apokryfos
– apokryfos, Commented Jan 26, 2017 at 15:21

Mouradif · Accepted Answer · 2017-01-26 17:14:37Z

3

As pointed out by @cHao ans @Kulvar, your "3" element is in fact "3\n" because your line returned by fgets ends with a \n which is normal.

Replace $a = explode(" ",$a_temp); with $a = explode(" ",trim($a_temp)); and you're fixed. Works with any string, numeric or not

answered Jan 26, 2017 at 17:14

Mouradif

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Comments

ʰᵈˑ · Accepted Answer · 2017-01-26 17:05:21Z

1

It seems you have a non-integer value in there. Use array_map() to cast all values to integers.

$a_temp = fgets($handle);
$a = explode(" ",$a_temp);
$a = array_map("intval", $a); //Cast all values to integers
for($i = 0; $i < 2; $i++){
    print_r($a);
    array_unshift($a, array_pop($a));
    print_r($a);
}

https://eval.in/724912

answered Jan 26, 2017 at 17:05

ʰᵈˑ

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4 Comments

JackSlayer94 Over a year ago

Yes casting fixed it! Thanks!

Mouradif Over a year ago

yes casting fixed it but that's not the correct answer. What if your file contains a b c instead of 1 2 3 ? This answer will not work.

JackSlayer94 Over a year ago

No its guaranteed to be an int and there is one more answer that works on string as he trims it.

ʰᵈˑ Over a year ago

@KiJéy yep, good point. I'd recommend OP accept your answer instead if it's strings.

Phil · Accepted Answer · 2018-10-18 12:50:01Z

1

Combine the array_push() and array_shift() function. In this solution you would have to input a number of rotations, or you change the $k variable in the for-loop to your desired amount of rotations.

for($i=0; $i<$k; $i++){

    //remove first element
    $firstElement = array_shift($a);

    //push first element to the end
    array_push($a, $firstElement);

}

echo implode(" ", $a);

edited Oct 18, 2018 at 12:50

answered Jan 15, 2018 at 7:46

Phil

196 bronze badges

Comments

Vinoth Kumar · Accepted Answer · 2020-01-15 17:29:36Z

The first method is the optimised code. But other two are solution but not optimise as the first one.

function rotate_left_method_1( $a, $d ) {
    $first  = array_slice( $a, 0, $d );
    $second = array_slice( $a, $d, null );

    return array_merge( $second, $first );
}

function rotate_left_method_2( $a, $d ) {
    $swap = 1;
    foreach ( $a as $v ) {
        if ( $d >= $swap ) {
            array_shift( $a );
            array_push( $a, $v );
            $swap ++;
        }
    }
    return $a;
}

function rotate_left_method_3( $a, $d ) {
    if ( is_array( $a ) ) {
        for ( $swap = 0; $swap < $d; $swap ++ ) {
            $temp = $a[0];
            array_shift( $a );
            array_push( $a, $temp );
        }
    }

    return $a;
}




var_dump( rotate_left_method_1( array( 1, 2, 3, 4, 5 ), 4 ) );
var_dump( rotate_left_method_2( array( 1, 2, 3, 4, 5 ), 4 ) );
var_dump( rotate_left_method_3( array( 1, 2, 3, 4, 5 ), 4 ) );

Mohammed Ammar · Accepted Answer · 2021-02-25 15:11:40Z

0

function rotateLeft($d, $arr) {
    $remaining = array_slice($arr, $d);
    array_splice($arr, $d);
    return array_merge($remaining,$arr);
}
$d =4; $arr = [1,2,3,4,5];
$result = rotateLeft($d, $arr);
var_dump($result);
output [5, 1, 2, 3, 4]

answered Feb 25, 2021 at 15:11

Mohammed Ammar

11 bronze badge

2 Comments

Syscall Over a year ago

Thank you for this code snippet, which might provide some limited, immediate help. A proper explanation would greatly improve its long-term value by showing why this is a good solution to the problem and would make it more useful to future readers with other, similar questions. Please edit your answer to add some explanation, including the assumptions you’ve made.

Mohammed Ammar Over a year ago

array_shift() modifies the original array and can be pretty slow because it needs to completely reindex the array

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