PHP Quick Sort Quicksort instance detailed _php skill

This example describes the PHP quick sort quicksort. Share to everyone for your reference, specific as follows:

Quicksort

In the fast sorting algorithm, the divide-and-conquer strategy is used. First, the sequence is divided into two sub sequences, recursively sorted, until the whole sequence is sorted. (That is, the thought in Split)

The steps are as follows:

Select a key element in the sequence as the axis;

The sequence is reordered to move elements smaller than the axis to the front of the axis, and the elements larger than the axis move to the back of the axis. After dividing, the shaft is in its final position;

Recursively reorder two subsequence: A subsequence containing a smaller element and a subsequence containing a larger element.

such as sequence $arr:

5 3 0 11 44 7 23 2 The first element $arr[0] = 5 as the axis setting flag bit low ... top stands for both end and end
2 3 0 11 44 7 23 2 starting from the opposite direction (right) comparison: 2<5 replaces the first position with the 2,low++
2 3 0 11 44 7 23 The comparison begins in the opposite direction (left) until: 5<11 replaces the last position with the 11,top–
Repeat the above steps until Low = top replaces the position with an axis element that is 5
2 3 0 5 44 7 23 11
This can be divided into two parts 2 3 0 and 44 23 11
So that we can get the recursion to proceed with the steps

Algorithm implementation:

 class quick_sort{function quicksort (& $arr, $low, $top) {if ($low < $top) {
        $pivotpos = $this->partition ($arr, $low, $top);
        $this->quicksort ($arr, $low, $pivotpos-1);
      $this->quicksort ($arr, $pivotpos +1, $top);
      } function partition (& $arr, $low, $top) {if ($low = = $top) {return;
      //Set the initial numeric $com = $arr [$low];
          while ($low!= $top) {//will replace the initial value to the left while ($top && $top!= $low) {if ($com > $arr [$top]) {
          $arr [$low + +] = $arr [$top];
          Break
          }else{$top--;
            }//will replace the initial value to the right while ($low && $low!= $top) {if ($com < $arr [$low]) {
            $arr [$top--] = $arr [$low];
          Break
          }else{$low + +;
      $arr [$low] = $com;
    return $low; }
}

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