确保 php 中相同的数组项不相邻

Question

I am struggling with this case. I have a random array that similar items can be in the next to each other and I don't want it to happen.

Example:

array("red","red","blue","green","green","blue");

Expected Output : array("red","blue","red","green","blue","green")

So I was thinking about shuffle the items until there are no similar items in the next to each other. But it will take a lot of time if the array has a lot of values.

Is there any effective way to make it happen?

Any help would be appreciated. Thanks

Answer 1

Just an idea:

• Shuffle the original array.
• Compare the first two. If they are the same, swap second with the last.
• Move to the next pair.
• Repeat until end reached.

Here we assume the worst case shuffle having the same values next together.

$colors = ["red", "red", "blue", "blue", "green", "green"];

for ($i = 0; $i < count($colors) - 1; $i++) {
    if ($colors[$i] !== $colors[$i + 1]) continue;
    $last = $colors[count($colors) - 1];
    $colors[count($colors) - 1] = $colors[$i];
    $colors[$i + 1] = $last;
}

print_r($colors);

Array
(
    [0] => red
    [1] => green
    [2] => blue
    [3] => red
    [4] => green
    [5] => blue
)

Answer 2

I ended up re-arrange to a new array. For those who have the same problem with me here is how I do it:

<?php

$colors = ["red","red","red","red","red","red","blue","blue","green","green","green","green","green","green","red","red","red"];
$newColors = array();

$uniqColors = array_values(array_unique($colors));

$countUniqColors = count($uniqColors);

$y = 0;

for ($i = 0; $i <= count($colors) - 1; $i++) {
    $newColors[$i] = $uniqColors[$y];
    $y += 1;
    if ($y >= $countUniqColors) $y = 0; 
}

print_r($newColors);

?>

I think this is the most effective way I can think of. Let me know if you have any thought about this solution

Answer 3

Just another idea:

• Take the array and scan from start to end
• Compare the next with current, when not equal, then continue
• Compare the next with current, when equal, search the next different and swap next with next different

Based on your comment of an even more worse case than in the original question, I suggest trying this, ensuring never one word will be twice next together.

$colors = ["red", "red", "red", "red", "red", "red", "blue", "blue", "green", "green", "green", "green", "green", "green", "red", "red", "red"];

for ($i = 0; $i < count($colors) - 1; $i++) {
    if ($colors[$i] !== $colors[$i + 1]) continue;

    for ($k = $i + 2; $k < count($colors) - 1; $k++) {
        if ($colors[$i + 1] === $colors[$k]) continue;
        $tmp = $colors[$i + 1];
        $colors[$i + 1] = $colors[$k];
        $colors[$k] = $tmp;
        break;
    }
}

print_r($colors);

Array
(
    [0] => red
    [1] => blue
    [2] => red
    [3] => blue
    [4] => red
    [5] => green
    [6] => red
    [7] => green
    [8] => red
    [9] => green
    [10] => red
    [11] => green
    [12] => red
    [13] => green
    [14] => red
    [15] => green
    [16] => red
)