PHP sorting algorithm implementation summary

This time I will bring you a summary of the implementation of the PHP sorting algorithm. What are the precautions for the implementation of the PHP sorting algorithm. The following is a practical case, let's take a look.

The examples in this article describe the implementation and efficiency analysis of four sorting algorithms in PHP. Share it with everyone for your reference, the details are as follows:

PHP’s four basic sorting algorithms are: Bubble sort, insertion sort, Selection sort and quick sort.

The following is the algorithm code I compiled:

1. Bubble sorting:

Idea: perform multiple rounds of bubbles on the array, each In one round, the elements in the array are compared pairwise, the positions are adjusted, and the largest number emerges.

//简单版：
function bubbleSort($arr)
{
   $n = count($arr);
   for($i=1;$i<$n;$i++) { //冒泡的轮数(最多$n-1轮)
     for($j=0;$j<$n-1;$j++) { //每一轮冒泡(两两比较，大者后移)
       if($arr[$j] > $arr[$j+1]) { //前者大于后者，交换位置
          $tmp = $arr[$j];
          $arr[$j] = $arr[$j+1];
          $arr[$j+1] = $tmp;
       }
     }
   }
   return $arr;
}

//改进版：
function bubbleSort($arr)
{
   $n = count($arr);
   for($i=1;$i<$n;$i++) { //冒泡的轮数(最多$n-1轮)
     $flag = 0;  //是否发生位置交换的标志
     for($j=0;$j<$n-$i;$j++) { //每一轮冒泡(两两比较，大者后移)
       if($arr[$j] > $arr[$j+1]) { //前者大于后者，交换位置
          $tmp = $arr[$j];
          $arr[$j] = $arr[$j+1];
          $arr[$j+1] = $tmp;
          $flag = 1;
       }
     }
     if($flag == 0) {  //没有发生位置交换，排序已完成
       break;
     }
   }
   return $arr;
}

In order to improve the efficiency of the bubble sorting algorithm, the main areas that need improvement are:

(1) Reduce the number of rounds of bubbles: when no position exchange occurs in a round of bubble sorting indicates that the array has been sorted and the loop should be exited immediately.

(2) Reduce the number of comparisons in each round: no longer compare some of the elements in the array that have been sorted.

2. Insertion sort:

Idea: Assume that the elements in front of the array are sorted, Traverse the elements at the back of the array, after the elements have been Find the appropriate position in the sorted element queue and insert it into it.

function insertSort($arr)
{
   $n = count($arr);
   for($i=1;$i<$n;$i++) { //从第二个元素开始插入
     for($j=$i-1;$j>=0;$j--) { //与前面的数比较，找到插入的位置
       if($arr[$j] > $arr[$j+1]) { //比前面的数小，交换位置
          $tmp = $arr[$j];
          $arr[$j] = $arr[$j+1];
          $arr[$j+1] = $tmp;
       } else { //大于或等于前面的数，表示已找到插入的位置
          break;
       }
     }
   }
   return $arr;
}

3. Selection sorting:

Idea: Make multiple selections, and each time select the largest element and put it in the specified position.

function selectSort($arr)
{
   $n = count($arr);
   for($i=$n-1;$i>0;$i--) { //选择排序的轮数($n-1轮)
     $pos = $i; //假设最大元素的位置
     for($j=0;$j<$i;$j++) { //每一轮：从未选择过的元素中选择最大的数
       if($arr[$j] > $arr[$pos]) { //所在位置元素比目前最大元素大，标志其位置
          $pos = $j;
       }
     }
     if($pos != $i) { //将最大元素放入指定的位置
       $tmp = $arr[$pos];
       $arr[$pos] = $arr[$i];
       $arr[$i] = $tmp;
     }
   }
   return $arr;
}

4. Quick sort:

Idea: recursive algorithm. First select the first element of the array as the standard, then put the numbers less than or equal to it and greater than it into two arrays respectively, perform the same processing on the two arrays, and finally merge the two arrays with the first elements.

function quickSort($arr)
{
   $n = count($arr);
   if($n  $cur) {
       $largeArr[] = $arr[$i];
     } else {
       $smallArr[] = $arr[$i];
     }
   }
   //分别对大数组和小数组进行相同的处理
   $smallArr = quickSort($smallArr);
   $largeArr = quickSort($largeArr);
   //合并小数组、分类基数和大数组
   return array_merge($smallArr,array($cur),$largeArr);
}

The time complexity and space complexity of each sorting algorithm:

The sorting algorithm	is the best Time analysis	Worst time analysis	Average time complexity	Stability	Space complexity
Bubble sort	O(n)	O(n2)	O(n2)	Stable	O(1)
Insertion sort	O(n)	O(n2)	O(n2)	Stable	O(1)
Selection sort	O(n2)	O(n2)	O(n 2)	Stable	O(1)
Quick sort	O(nlog2n)	O(n2)	O(nlog2n)	Unstable	O(log2n)~O(n)

Note: Quick sort is most efficient when the array is out of order. The efficiency is worst when the array is sorted.

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