PHP common algorithms and time complexity

This article introduces in detail the commonly used algorithms and time complexity in PHP. Friends in need can refer to it

Arranged in increasing order of magnitude. Common time complexity is: constant order O(1 ), logarithmic order O(log2n), linear order O(n), linear logarithmic order O(nlog2n), square order O(n2), cubic order O(n3)

代码如下:

//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.&#39;/*&#39;) 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;
}

代码如下：
/**
 * 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);

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Smart use of arrays in PHP to reduce the time complexity of programs

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