PHP iteration and Recursion implement unlimited classification, and php recursion is unlimited

PHP iteration and Recursion implement unlimited classification, and php recursion is unlimited

Infinitus classification is a common situation in development. Therefore, this article summarizes and summarizes the common infinitus classification algorithms.

1. Implement loop iteration

$ Arr = [1 => ['id' => 1, 'name' => 'parent 1', 'Father '=> NULL], 2 => ['id' => 2, 'name' => 'parent 2', 'Father '=> NULL], 3 => ['id' => 3, 'name' => 'parent 3', 'Father '=> NULL], 4 => ['id' => 4, 'name' => 'children 1-1 ', 'Father '=> 1], 5 => ['id' => 5, 'name' => 'children 1-2', 'Father '=> 1], 6 => ['id' => 6, 'name' => 'children 1-3 ', 'Father' => 1], 7 => ['id' => 7, 'name' => 'er 2-1 ', 'Father' => 2], 8 => ['id' => 8, 'name' => 'er 2-1 ', 'Father '=> 2], 9 => ['id' => 9, 'name' => 'er 3-1', 'Father' => 3], 10 => ['id' => 10, 'name' => 'children 3-1-1 ', 'Father' => 9], 11 => ['id' => 11, 'name' => 'children 1-1-1 ', 'Father' => 4], 12 => ['id' => 12, 'name' => 'children 2-1-1 ', 'fatsher' => 7],]; function generateTree ($ items) {$ tree = array (); foreach ($ items as $ item) {if (isset ($ items [$ item ['father ']) {$ items [$ item ['father '] ['son'] [] = & $ items [$ item ['id'];} else {$ tree [] = & $ items [$ item ['id'] ;}} return $ tree ;}$ tree = generateTree ($ arr ); print_r (json_encode ($ tree ));

Output:

Analysis:

This algorithm uses loop iteration to output linear structures in a tree structure according to the parent-child relationship. The key of the algorithm is to use references.

Advantage: fast and efficient.

Disadvantage: the key value of the array must be the same as the id value, so it is not easy to retrieve data (also use iteration to obtain data)

2. Recursive Implementation

$ Arr = [0 => ['id' => 1, 'name' => 'parent 1', 'Father '=> 0], 1 => ['id' => 2, 'name' => 'parent 2', 'Father '=> 0], 2 => ['id' => 3, 'name' => 'parent 3', 'Father '=> 0], 3 => ['id' => 4, 'name' => 'children 1-1 ', 'Father '=> 1], 4 => ['id' => 5, 'name' => 'children 1-2', 'Father '=> 1], 5 => ['id' => 6, 'name' => 'children 1-3 ', 'Father' => 1], 6 => ['id' => 7, 'name' => 'er 2-1 ', 'Father' => 2], 7 => ['id' => 8, 'name' => 'er 2-1 ', 'Father '=> 2], 8 => ['id' => 9, 'name' => 'er 3-1', 'Father' => 3], 9 => ['id' => 10, 'name' => 'children 3-1-1 ', 'Father' => 9], 10 => ['id' => 11, 'name' => 'children 1-1-1 ', 'Father' => 4], 11 => ['id' => 12, 'name' => 'children 2-1-1 ', 'fatsher' => 7],]; function generateTree ($ arr, $ id, $ step) {static $ tree = []; foreach ($ arr as $ key => $ val) {if ($ val ['father '] = $ id) {$ flg = str_repeat ('employee ―', $ step); $ val ['name'] = $ flg. $ val ['name']; $ tree [] = $ val; generateTree ($ arr, $ val ['id'], $ step + 1 );}} return $ tree;} $ tree = generateTree ($ arr, 0, 0); foreach ($ tree as $ val) {echo $ val ['name']. '<br> ';}

Output:

Analysis:

Recursion is used. The key value and id value of the array can be different. Finally, the array is output in order.

Advantage: convenient traversal and searching for parent and child elements

Disadvantage: php is not good at recursion, and the efficiency will be significantly reduced when the data volume is large.

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