Simple sorting of the PHP sorting algorithm (easy Selection sort)

This article mainly introduced the PHP sorting algorithm's Simple choice sort (easy Selection sort), combined with the example form more detailed analysis the simple choice sorting algorithm principle and the related realization skill, needs the friend to refer to the next

In this paper, we describe the simple selection of the PHP sorting algorithm (Selection sort). Share to everyone for your reference, as follows:

Basic idea:

Through the comparison between the N-i keyword, the smallest record of the keyword is selected from the N-i + 1 records and exchanged with the first (1 <= i <= N) records, and the sequence of records is completed after the n-1 trip.

Algorithm implementation:

<?php//Simple selection sort//Swap functions function Swap (array & $arr, $a, $b) {  $temp = $arr [$a];  $arr [$a] = $arr [$b];  $arr [$b] = $temp;} Simple selection sorting algorithm function Selectsort (array & $arr) {  $count = count ($arr);  for ($i = 0; $i < $count-1; $i + +) {    //record all elements after $i element minimum subscript    $min = $i;    for ($j = $i + 1; $j < $count; $j + +) {      if ($arr [$j] < $arr [$min]) {        $min = $j;      }    }    if ($min! = $i) {      swap ($arr, $min, $i);}}}  $arr = Array (9,1,5,8,3,7,4,6,2); Selectsort ($arr); Var_dump ($arr);

Operation Result:

Array (9) {[0]=> int (1) [1]=> int (2) [2]=> int (3) [3]=> int (4) [4]=> int (5) [5]=> int (6) [6]=> Int (7) [7]=> Int (8) [8]=> int (9)}

Analysis of Complexity:

You need to move records less often during simple selection sorting. In the best case, the initial state of the records to be sorted is already in a positive order, so you do not need to move the records.

In the worst case, the initial state of the records to be sorted is the largest of the first records, and then the records are ordered from small to large, and the maximum number of times to move Records is 3 (n-1). Simple selection The number of comparisons that need to be made in the sort process is independent of the arrangement of the sequence of records to be sorted in the initial state. When I=1, a n-1 comparison is required, and n-2 comparisons are required when i=2, and so on, the total number of comparisons required is (n-1) + (n-2) +...+2+1=n (n-1)/2, that is, the time complexity of the comparison operation is O (n^2), The time complexity of the move operation is O (n).

Simple selection sorting is an unstable sort.

This article refers to from the "Big Talk Data Structure", in this only record, convenient to consult later, great God do not spray!