Detailed analysis of selection sort algorithm

Selection sort

Selection sort is one of the most stable sorting algorithms. When using it, the smaller the data size, the better. Theoretically speaking, selection sort may also be the most common method that most people think of when sorting.

Selection sort is a simple and intuitive sorting algorithm. How it works is:

Traverse an array, and in the process, find the maximum value and its position in the array. Then "swap the position" of the unit with the maximum value with the last unit of the array. After doing this, the maximum value in the array must be placed at the last position.

Continue to traverse the remaining data in the above process and do the same thing. At this time, the maximum value of the remaining part can also be placed at the last position of the remaining part - it is the penultimate position as a whole. s position.

So on and so forth. . . . . .

Illustration:

##Original array 18221215239First trip18221215923##Second tripThe third tripThe fourth trip##The fifth trip91215182223# #The code is as follows:

18	9	12	15	22	23
15	9	12	18	22	23
12	9	15	18	22	23

<?php
        $arr1 = array(18,22,12,15,23,9);
        $n = count($arr1);
        for ($i=0; $i < $n-1; $i++) { 
            //找最大值
            $max = $arr1[0];
            $max_key = 0;
            for ($k=0; $k < $n - $i; $k++) { 
                if ($arr1[$k] > $max) {
                    $max = $arr1[$k];
                    $max_key = $k;
                }
            }
            //交换
            $temp = $arr1[$max_key];
            $arr1[$max_key] = $arr1[$n-1-$i];
            $arr1[$n-1-$i] = $temp;
        }

Summary of the rules:

1. To find the largest one from beginning to end value (and subscript), and the number of times to exchange is $n-1, $n is the length of the array 2. What each time needs to do is: a) find the maximum value, right) and Exchange the maximum value with the last item of this trip;

3. The number of data to find the maximum value in each trip is 1 less than the previous trip, of which the first trip has $n indivual.

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