常用演算法和時間複雜度（php）

按數量級遞增排列，常見的時間複雜度有：常數階O(1),對數階O(log2n),線性階O(n),線性對數階O(nlog2n),平方階O(n2)，立方階O(n3)

//二分尋找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($a,0,5,1));//遍曆目錄O(log2n)function bianli($p){$a = array();foreach (glob($p.'/*') as $f){if(is_dir($f)){$a = array_merge($a,bianli($f));}else{$a[] = $f;}}return $a;}//階乘O(log2n)function jc($n){if($n<=1){return 1;}else{return $n*jc($n-1);}}//快速尋找  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 $a;}//選擇排序O(N*N)function xuanze($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;}