PHPer无限极分类算法

无限级分类是开发中常见的情况,也经常会在面试,主考官问到,笔试中遇到,因此本文对常见的无限极分类算法进行总结归纳,其实大多数就是迭代与递归。

1.循环迭代实现

<?php
$arr = [
  1=>['id'=>1,'name'=>'父1','father'=>NULL],
  2=>['id'=>2,'name'=>'父2','father'=>NULL],
  3=>['id'=>3,'name'=>'父3','father'=>NULL],
  4=>['id'=>4,'name'=>'儿1-1','father'=>1],
  5=>['id'=>5,'name'=>'儿1-2','father'=>1],
  6=>['id'=>6,'name'=>'儿1-3','father'=>1],
  7=>['id'=>7,'name'=>'儿2-1','father'=>2],
  8=>['id'=>8,'name'=>'儿2-1','father'=>2],
  9=>['id'=>9,'name'=>'儿3-1','father'=>3],
  10=>['id'=>10,'name'=>'儿3-1-1','father'=>9],
  11=>['id'=>11,'name'=>'儿1-1-1','father'=>4],
  12=>['id'=>12,'name'=>'儿2-1-1','father'=>7],
];
function generateTree($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));

分析:

这个算法利用了循环迭代,将线性结构按照父子关系以树形结构输出,算法的关键在于使用了引用.

优点:速度快,效率高.

缺点:数组的key值必须与id值相同,不便于取出数据(同样使用迭代获取数据)

2.递归实现

$arr = [
  0=>['id'=>1,'name'=>'父1','father'=>0],
  1=>['id'=>2,'name'=>'父2','father'=>0],
  2=>['id'=>3,'name'=>'父3','father'=>0],
  3=>['id'=>4,'name'=>'儿1-1','father'=>1],
  4=>['id'=>5,'name'=>'儿1-2','father'=>1],
  5=>['id'=>6,'name'=>'儿1-3','father'=>1],
  6=>['id'=>7,'name'=>'儿2-1','father'=>2],
  7=>['id'=>8,'name'=>'儿2-1','father'=>2],
  8=>['id'=>9,'name'=>'儿3-1','father'=>3],
  9=>['id'=>10,'name'=>'儿3-1-1','father'=>9],
  10=>['id'=>11,'name'=>'儿1-1-1','father'=>4],
  11=>['id'=>12,'name'=>'儿2-1-1','father'=>7],
];
function generateTree($arr,$id,$step){
  static $tree=[];
  foreach($arr as $key=>$val) {
    if($val['father'] == $id) {
      $flg = str_repeat('└―',$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>';
}

分析:

利用了递归,数组的key值与id值可以不相同,最后以顺序的结构输出数组 优点:方便遍历,查找父子元素 缺点:php不擅长递归,数据量大的情况下效率会显著降低

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