How Can We Efficiently Merge Two Flat Arrays Alternately?

Merging Flat Arrays Alternately

Given two flat arrays of equal size, we strive to merge them alternately, preserving the order of elements within each array. The desired output resembles:

array(0, 3, 1, 4, 2, 5);

While a brute force approach like the following accomplishes the task:

for (var $i = 0; $i < count($a1); $i++) {
    newArray[] = $a1[$i];
    newArray[] = $b1[$i];
}

Efficiency becomes crucial when performing this operation thousands of times.

A Native Solution

The suggested native solution involves a tailored loop that iterates over the arrays and appends their elements alternately to a new array:

$count = count($a1);
for ($i = 0; $i < $count; $i++) {
    $newArray[] = $a1[$i];
    $newArray[] = $b1[$i];
}

This technique proves more efficient, particularly when repeated numerous times, as demonstrated by the benchmark test below:

$a1 = array(0,1,2);
$a2 = array(3,4,5);

$start = microtime(TRUE);

for($t = 0; $t < 100000; $t++)
{
    $newArray = array();
    $count = count($a1);
    for ($i = 0; $i < $count; $i++)
    {
        $newArray[] = $a1[$i];
        $newArray[] = $b1[$i];
    }
}
echo  round(microtime(TRUE) - $start, 2); # 0.6

$a1 = array(0,1,2);
$a2 = array(3,4,5);

$start = microtime(TRUE);

for($t = 0; $t < 100000; $t++)
{
    $newArray = array();
    for ($i = 0; $i < count($a1); $i++)
    {
        $newArray[] = $a1[$i];
        $newArray[] = $a2[$i];
    }
}
echo  round(microtime(TRUE) - $start, 2); # 0.85

Therefore, pre-counting the array size provides approximately a 25% performance boost, making it the optimal solution for large-scale operations.

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