Turn list with parent ID into tree, id list Tree _php tutorial

Turn list with parent ID to tree, ID list to tree

We know that databases generally store trees in a list (id,pid). How to extract the tree? The simplest method is to check the table according to the PID loop. But there is no doubt that this creates a huge database query overhead.

Then the general recommended method is to isolate all relevant data at once, but this involves a problem, how to build a tree quickly.

I used to think that this is a complex operation that requires at least one recursion, and the time complexity will not be O (n).

Some time ago, a job needs to solve this problem. I thought about it and found that it was possible to solve this problem through a single-layer loop, which was achieved as follows:

1 functionList2tree ($listItem,$idx= ' id ',$PIDX= ' pid ',$childKey= ' list '){2     $map=Array();3     $pMap=Array();4 5     foreach($listItem  as $item){6         $id=$item[$idx];7         $pid=$item[$PIDX];8         $map[$id] = &$item;9         unset($item);Ten     }        One              A     foreach($map  as $id= &$item){ -         $pid=$item[$PIDX]; -         $item[$childKey] =Array(); the  -         if(!isset($map[$pid])){ -             $pMap[$id] = &$item;  -         }        +         Else{    -             $pItem= &$map[$pid]; +             $pItem[$childKey[] = &$item; A         }    at  -         unset($item,$pItem); -     } -     -     return Array_shift($pMap); -}

Test it:

1 //path for easy identification of parent-child relationships2 $json= <<<JSON3 [4     {5"id": 2,6"pid": 1,7"Path": "/se"8},9     {Ten"id": 3, One"pid": 2, A"Path": "/se/4901" -}, -     { the"id": 4, -"pid": 5, -"Path": "/se/4901/mask/query" -}, +         { -"id": 5, +"pid": 3, A"Path": "/se/4901/mask" at}, -     { -"id": 6, -"pid": 2, -"Path": "/se/4902" -}, in     { -"id": 7, to"pid": 6, +"Path": "/se/4902/mask" -     } the ] * JSON; $ Panax Notoginseng $list= Json_decode ($json,true); -  the Var_dump(List2tree ($list));

Results:

Array(4) {  ["id"]=>Int (2)  ["pid"]=>Int (1)  ["Path"]=>string(3) "/se"  ["List"]=>Array(2) {    [0]=>Array(4) {      ["id"]=>Int (3)      ["pid"]=>Int (2)      ["Path"]=>string(8) "/se/4901"      ["List"]=>Array(1) {        [0]=>Array(4) {          ["id"]=>Int (5)          ["pid"]=>Int (3)          ["Path"]=>string(+) "/se/4901/mask"          ["List"]=>Array(0) {          }        }      }    }    [1]=>Array(4) {      ["id"]=>Int (6)      ["pid"]=>Int (2)      ["Path"]=>string(8) "/se/4902"      ["List"]=>Array(1) {        [0]=>Array(4) {          ["id"]=>Int (7)          ["pid"]=>Int (6)          ["Path"]=>string(+) "/se/4902/mask"          ["List"]=>Array(0) {          }        }      }    }  }}

Succeeded in turning the list into a tree

http://www.bkjia.com/PHPjc/1102845.html www.bkjia.com true http://www.bkjia.com/PHPjc/1102845.html techarticle Convert list with parent ID to tree, ID list to tree we know that a database is generally saved as a list (id,pid). How to extract the tree? The simplest way to do this is by ...

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