php 冒泡排序

<?php// ==============PHP 冒泡算法==============header("Content-type:text/html;charset=utf-8"); $arr=array(1,11,10,12,21,3);  function mpsort($arr){      $n = count($arr);      for($i = 0; $i < $n; $i++){  //循环总的次数。          for($j = 0; $j < $n-$i-1; $j++){               if($arr[$j] > $arr[$j+1]){    //判断前一个数是否大于第二个数                  $tmp = $arr[$j];        //这三步是 调换位置     自然排序 1 2 3 12 13                   $arr[$j] = $arr[$j+1];                  $arr[$j+1] = $tmp;              }          }      }      return $arr;  }  echo '<pre>';  print_r(mpsort($arr));  echo '</pre>';  //   ==================== 原理讲解======================/*$arr=array(5,4,2,1,3);  print_r(mpsort($arr));  function mpsort($arr){    $n = count($arr);    $num = 1;    for ($i=0; $i < $n; $i++) {           for ($j=0; $j < $n-$i-1; $j++) {              if($arr[$j] > $arr[$j+1] ){                  print_r($arr);                  echo  $num++;                  echo "<br>";                  $tmp = $arr[$j];                  $arr[$j]  = $arr[$j+1];                  $arr[$j+1] = $tmp;              }else{                print_r($arr);                echo "-----未处理------  ";                echo $num++;                echo "<br>";              }          }    }}*/// $i     0  1  2  3  4    $i  出现的值。// $j <  4  3  2  1  0    $j 出现的值。     总共循环10次。/*  打印出来每一次执行的情况。Array ( [0] => 5 [1] => 4 [2] => 2 [3] => 1 [4] => 3 ) 1Array ( [0] => 4 [1] => 5 [2] => 2 [3] => 1 [4] => 3 ) 2Array ( [0] => 4 [1] => 2 [2] => 5 [3] => 1 [4] => 3 ) 3Array ( [0] => 4 [1] => 2 [2] => 1 [3] => 5 [4] => 3 ) 4Array ( [0] => 4 [1] => 2 [2] => 1 [3] => 3 [4] => 5 ) 5Array ( [0] => 2 [1] => 4 [2] => 1 [3] => 3 [4] => 5 ) 6Array ( [0] => 2 [1] => 1 [2] => 4 [3] => 3 [4] => 5 ) 7Array ( [0] => 2 [1] => 1 [2] => 3 [3] => 4 [4] => 5 ) 8Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) -----未处理------ 9Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 ) -----未处理------ 10*//*第二个for循环中的 $n-$i-1  设定原因，比如现在索引在2（从0开始），那么后面还有2个值需要比较。那么$j的for循环只要在对比2次就可以了（$j 的值是增加的）。那数组的第 $j 个索引，和 $j+1 个索引值大小作对比，然后根据大小确定是否调整位置，完成之后会进入到for循环下一个$j索引值，继续对比。*/