A detailed description of the direct selection sequence of the PHP sorting algorithm series

This article is mainly for the introduction of the PHP sorting algorithm series of direct selection of relevant data, with a certain reference value, interested in small partners can refer to

Direct Select sort

The basic idea of direct selection sorting (straight select sorting) is to select the minimum value from r[0]~r[n-1], to switch to r[0], to select the smallest value from r[1]~r[n-1] for the first time, and to switch to r[1], ...., i-th from r[i-1]~ R[n-1], select the minimum value, and r[i-1] exchange, ..., the n-1 time from r[n-2]~r[n-1] to select the minimum value, and r[n-2] exchange, a total of n-1 times, to get a sort code from small to large order sequence ·

The main advantages of selecting a sort are related to data movement. If an element is in the correct final position, it will not be moved. Select sort every time a pair of elements is exchanged, at least one of them will be moved to its final position, so the table of n elements is sorted for a total of up to n-1 times. In all of the sorting methods that rely entirely on swapping to move elements, choosing a sort is a very good one.

Principle

First find the smallest (large) element in the unordered sequence, place it at the beginning of the sort sequence, and then continue looking for the smallest (large) element from the remaining unsorted elements, and place it at the end of the sorted sequence. And so on until all elements are sorted.

Example

Set the array to a[0...n-1].
1. Initially, the array is all unordered area is a[0..n-1]. Make I=0
2. Select a minimal element in the unordered area a[i...n-1] and swap it with a[i]. After the exchange, A[0...I] formed an orderly area.
3.i++ and repeat the second step until the i==n-1. Sorting is complete.

Example

Sorting an array [53,89,12,98,25,37,92,5]

First Take i=0;a[i] as the minimum value, compare the latter value with A[i], if smaller than a[i], then the a[i] Exchange location, $i + +

[5,89,53,98,25,37,92,12]

First Take i=1;a[i] as the minimum value, compare the latter value with A[i], if smaller than a[i], then the a[i] Exchange location, $i + +

[5,12,89,98,53,37,92,25]

Repeat the above steps

PHP Code implementation

function Select_sort ($arr) {  $length =count ($arr);  for ($i =0; $i < $length-1; $i + +) {    for ($j = $i +1, $min = $i; $j < $length; $j + +) {      if ($arr [$min]> $arr [$j]) {        $min = $j;      }    }    $temp = $arr [$i];    $arr [$i]= $arr [$min];    $arr [$min]= $temp;  }  return $arr;}