How to create a binary tree in php (code example)

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1. Use the principle of recursion, except that where the node was originally printed, it is changed to the operation of generating the node and assigning a value to the node
if(ch=='#' ){*T=NULL;}else{malloc();(*T)->data=ch;createFunc((*T)->lchild);createFunc((*T)->rchild);}

2. Preorder traversal: visit the root node first, traverse the left subtree in preorder, traverse the right subtree in preorder; left and right in the middle

3. Put the values ​​of each node in the binary tree The null pointer leads to a virtual node whose value is a specific value#. The binary tree processed is an extended binary tree of the original binary tree. The extended binary tree achieves a traversal sequence to determine a binary tree

<?php
class BinTree{
        public $data;
        public $left;
        public $right;
}
//前序遍历生成二叉树
function createBinTree(){
        $handle=fopen("php://stdin","r");
        $e=trim(fgets($handle));
        if($e=="#"){
                $binTree=null;
        }else{
                $binTree=new BinTree();
                $binTree->data=$e;
                $binTree->left=createBinTree();
                $binTree->right=createBinTree();
        } 
        return $binTree;
}  
  
$tree=createBinTree();
  
var_dump($tree);
 
#
object(BinTree)#1 (3) {
  ["data"]=>
  string(1) "A"
  ["left"]=>
  object(BinTree)#2 (3) {
    ["data"]=>
    string(1) "B"
    ["left"]=>
    NULL
    ["right"]=>
    object(BinTree)#3 (3) {
      ["data"]=>
      string(1) "D"
      ["left"]=>
      NULL
      ["right"]=>
      NULL
    }
  }
  ["right"]=>
  object(BinTree)#4 (3) {
    ["data"]=>
    string(1) "C"
    ["left"]=>
    NULL
    ["right"]=>
    NULL
  }
}

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