PHP common algorithms and time complexity

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By order of magnitude, the common time complexity is: Constant order O (1), Logarithmic order O (log2n), linear order O (n), linear logarithmic order O (nlog2n), square O (n2), Cubic O (N3)

Copy Code code as follows:


//Two point search 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));


//Traverse tree 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;


}


//factorial O (log2n)


function JC ($n) {


if ($n <=1) {


return 1;


}else{


return $n *JC ($n-1);


}


}


//Quick Find 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);


}


//Insert sort 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;


}


//select sort 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;


}


//Bubble sort 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;


}

Copy Code code as follows:

/**
* Arrangement Combination
* Using the binary method of the combination of choice, such as the 5 selection of 3 o'clock, only 3 bits to 1 on it, so the combination can be 01101 11100 00111 10011 01110, such as 10 of the combination
*
* @param the array to be arranged $arr
* @param minimum number $min _size
* @return new array combinations that meet the criteria
*/
function Plzh ($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);