按数量级递增排列，常见的时间复杂度有：常数阶O(1),对数阶O(log2n),线性阶O(n),线性对数阶O(nlog2n),平方阶O(n2)，立方阶O(n3)

//二分查找O(log2n)
function erfen($a,$l,$h,$f){
    if($l >$h){ return false;}

    $m = intval(($l+$h)/2);

    if ($a[$m] == $f){
        return $m;
    }elseif ($f < $a[$m]){
        return erfen($a, $l, $m-1, $f);
    }else{
        return erfen($a, $m+1, $h, $f);
    }
    
}
$a = array(1,12,23,67,88,100);
var_dump(erfen($a,0,5,1));

//遍历树O(log2n)
function bianli($p){
    $a = array();
    foreach (glob($p.'/*') as $f){
        if(is_dir($f)){
            $a = array_merge($a,bianli($f));
        }else{
            $a[] = $f;
        }
    }
    return $a;
}


//阶乘O(log2n)
function jc($n){
    if($n<=1){
        return 1;
    }else{
        return $n*jc($n-1);
    }    
}
//快速查找  O(n *log2(n))
function kuaisu($a){
    $c = count($a);
    if($c <= 1){return $a;}
    $l = $r = array();    
    for ($i=1;$i<$c;$i++){
        if($a[$i] < $a[0]){
            $l[] = $a[$i];
        }else{
            $r[] = $a[$i];
        }
    }
    $l = kuaisu($l);
    $r = kuaisu($r);
    return array_merge($l,array($a[0]),$r);
}
//插入排序  O(N*N)
function charu($a){
  $c = count($a);
  for($i=1;$i<$c;$i++){
      $t = $a[$i];
      for($j=$i;$j>0 && $a[$j-1]>$t;$j--){
          $a[$j] = $a[$j-1];          
      }
      $a[$j] = $t;
  }
  return $a;
}

//选择排序O(N*N)
function xuanze($a){
    $c = count($a);
    for($i=0;$i<$c;$i++){
        for ($j=$i+1;$j<$c;$j++){
            if($a[$i]>$a[$j]){
                $t = $a[$j];
                $a[$j] = $a[$i];
                $a[$i] = $t;
             }
        }
    }
    return $a;
}
//冒泡排序   O(N*N)
function maopao($a){
    $c = count($a);
    for($i=0;$i<$c;$i++){
        for ($j=$c-1;$j>$i;$j--){
            if($a[$j] < $a[$j-1]){
               $t = $a[$j-1];
               $a[$j-1] = $a[$j];
               $a[$j] = $t;
            }
        }    
    }
    return $a;
} 

/**
 * 排列组合
 * 采用二进制方法进行组合的选择，如表示5选3时，只需有3位为1就可以了，所以可得到的组合是 01101 11100 00111 10011 01110等10种组合
 *
 * @param 需要排列的数组 $arr
 * @param 最小个数 $min_size
 * @return 满足条件的新数组组合
 */
function plzh($arr,$size=5) {
  $len = count($arr);
  $max = pow(2,$len);
  $min = pow(2,$size)-1;
  $r_arr = array();
  for ($i=$min; $i<$max; $i++){
   $count = 0;
   $t_arr = array();
   for ($j=0; $j<$len; $j++){
    $a = pow(2, $j);
    $t = $i&$a;
    if($t == $a){
     $t_arr[] = $arr[$j];
     $count++;
    }
   }   
   if($count == $size){
    $r_arr[] = $t_arr;    
   }   
  }
  return $r_arr;
 }

 

$pl = pl(array(1,2,3,4,5,6,7),5);

var_dump($pl);