Use PHP to implement four common sorting algorithms and their implementation principles

******Insertion sort (one-dimensional array)

1, starting from the first element, the element can be considered to have been sorted

2, take out the next element, after it has been sorted Scan the element sequence from back to front

3. If the element (sorted) is greater than the new element, move the element to the next position

4. Repeat step 3 until you find the sorted element that is less than or equal to the new element. The position of the element

5, insert the new element into this position

6, repeat step 2

*/

function insert_sort($arr)

{

$len = count($arr);

for ($i=1; $i<$len; $i++)

                                                                                                                                                                                                                  ] > $tmp && $j>=0)

                                                                $arr[$j +1] = $tmp;

}

Return $arr;

}

/*

****** Bubble sort (one-dimensional array)

1, compare adjacent elements. If the first one is bigger than the second one, swap them both.

2. Do the same work for each pair of adjacent elements, from the first pair at the beginning to the last pair at the end. At this point, the last element should be the largest number.

3. Repeat the above steps for all elements except the last one.

4. Continue to repeat the above steps for fewer and fewer elements each time until there are no pairs of numbers to compare. For ($j=$len-1; $j>$i; $j--)                                                                       $ tmp = $arr[$j-1];                                              }

}

  return $arr;

}

/*

******Selection sort (one-dimensional array)

1, first find the smallest element in the unsorted sequence and store it at the starting position of the sorted sequence ,

2, and then continue to find the smallest element from the remaining unsorted elements and put it at the end of the sorted sequence.

3, and so on until all elements are sorted.

*/

function select_sort($arr){

$count = count($arr);

for($i=0; $i<$count-1; $i++)

{

$ k = $i;

for($j=$i+1; $j<$count; $j++)

{

if ($arr[$k] > $arr[$j])

{

                                                                                                                                                                     $arr[$k];

  Dimension array)

1, first randomly pick a middle value

2, put the smaller value than the middle value on the left, and put the larger value than the middle value on the right side,

3, and then compare the left and right values ​​respectively. The side data recursively calls steps 1 and 2 to merge the left side, middle value, and right side data.

*/

function quick_sort($arr)

{

    if (count($arr) <= 1)

    {

        return $arr;

    }

    $key = $arr[0];

    $left_arr = array();

    $right_arr = array();

    for ($i=1; $i
    {

        if ($arr[$i] <= $key) $left_arr[] = $arr[$i];

        else  $right_arr[] = $arr[$i];

    }

    $left_arr = quick_sort($left_arr);

    $right_arr = quick_sort($right_arr);

    return array_merge($left_arr, $key, $right_arr);

}

$a = array(123,321,432,341345,45234,53,493);

echo "

";<br><br>print_r(select_sort($a));<br><br>print_r(bubble_sort($a));<br><br>print_r(insert_sort($a));<br><br>print_r(quick_sort($a));<br><br>echo "

";