标签：style blog http color 使用 os io 2014
归并排序法是一个基于分治法的比较排序方法，其最差情况复杂度为O(nlogn)，而快速排序法的复杂度在最差情况下达到O(n2)
本文使用PHP来讨论其算法过程：
假设对乱序数列进行排序
$input = array(11,5,1,4,8,7,9,2);
思路可以表示：（图是PPT画的，比较简单，请看官见谅）
比较的过程如下
贴上PHP代码：
1 <?php 2 $input = array(11,5,1,4,8,7,9,2); 3 function merge_sort($arr){ 4 if(count($arr)<=1){ 5 echo "return array:"; 6 print_r($arr); 7 echo "<br>"; 8 return $arr; 9 } 10 $left = array_slice($arr,0,(int)(count($arr)/2)); 11 $right= array_slice($arr,(int)(count($arr)/2)); 12 13 $left = merge_sort($left); 14 $right = merge_sort($right); 15 16 echo "Left: "; 17 print_r($left); 18 echo "<br>"; 19 echo "right: "; 20 print_r($right); 21 echo "<br>"; 22 23 $output = merge($left,$right); 24 25 return $output; 26 } 27 28 function merge($left,$right){ 29 echo "compare:"; 30 print_r($left); 31 print_r($right); 32 echo "<br><br>"; 33 34 $result = array(); 35 while(count($left)>0 && count($right)>0){ 36 if($left[0] <= $right[0]){ 37 array_push($result,array_shift($left)); 38 }else{ 39 array_push($result,array_shift($right)); 40 } 41 } 42 array_splice($result,count($result),0,$left); 43 array_splice($result,count($result),0,$right); 44 45 return $result; 46 } 47 print_r($input); 48 echo "<br>"; 49 $output = merge_sort($input); 50 echo "result:<br>"; 51 print_r($output); 52 ?>
贴上打印结果：
Array ( [0] => 11 [1] => 5 [2] => 1 [3] => 4 [4] => 8 [5] => 7 [6] => 9 [7] => 2 )
return array:Array ( [0] => 11 )
return array:Array ( [0] => 5 )
Left: Array ( [0] => 11 )
right: Array ( [0] => 5 )
compare:Array ( [0] => 11 ) Array ( [0] => 5 )
return array:Array ( [0] => 1 )
return array:Array ( [0] => 4 )
Left: Array ( [0] => 1 )
right: Array ( [0] => 4 )
compare:Array ( [0] => 1 ) Array ( [0] => 4 )
Left: Array ( [0] => 5 [1] => 11 )
right: Array ( [0] => 1 [1] => 4 )
compare:Array ( [0] => 5 [1] => 11 ) Array ( [0] => 1 [1] => 4 )
return array:Array ( [0] => 8 )
return array:Array ( [0] => 7 )
Left: Array ( [0] => 8 )
right: Array ( [0] => 7 )
compare:Array ( [0] => 8 ) Array ( [0] => 7 )
return array:Array ( [0] => 9 )
return array:Array ( [0] => 2 )
Left: Array ( [0] => 9 )
right: Array ( [0] => 2 )
compare:Array ( [0] => 9 ) Array ( [0] => 2 )
Left: Array ( [0] => 7 [1] => 8 )
right: Array ( [0] => 2 [1] => 9 )
compare:Array ( [0] => 7 [1] => 8 ) Array ( [0] => 2 [1] => 9 )
Left: Array ( [0] => 1 [1] => 4 [2] => 5 [3] => 11 )
right: Array ( [0] => 2 [1] => 7 [2] => 8 [3] => 9 )
compare:Array ( [0] => 1 [1] => 4 [2] => 5 [3] => 11 ) Array ( [0] => 2 [1] => 7 [2] => 8 [3] => 9 )
result:
Array ( [0] => 1 [1] => 2 [2] => 4 [3] => 5 [4] => 7 [5] => 8 [6] => 9 [7] => 11 )
标签：style blog http color 使用 os io 2014
原文地址：http://www.cnblogs.com/angular/p/3900580.html
