Binary Tree Level Order Traversal @LeetCode

PROBLEM :

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:
Given binary tree [3,9,20,null,null,15,7],
    3
   / \
  9  20
    /  \
   15   7
 
return its level order traversal as:
[
  [3],
  [9,20],
  [15,7]
]

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SIMPLE c++ IMPLEMENTATION :( Recursive Solution )
--------------------------------------------------------------------------------

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        int height=FindHeight(root) ;
       
        vector<vector<int>> vec(height,vector<int> {});
        LevelTraversal(root,vec,0) ;
        return vec ;
    }
   
    int FindHeight(TreeNode* root){
        if(root==NULL)
            return 0 ;
           
        int l=FindHeight(root->left) ;
        int r=FindHeight(root->right) ;
        return l>r?l+1:r+1 ;
    }
   
    void LevelTraversal(TreeNode* root,vector<vector<int>> &vec,int curr){
        if(root==NULL)
            return ;
           
        vec[curr].push_back(root->val);
           
        LevelTraversal(root->left,vec,curr+1) ;
        LevelTraversal(root->right,vec,curr+1) ;
    }
};

--------------------------------------------------------------------------------
SIMPLE c++ IMPLEMENTATION :( Iterative Solution - QUEUE )
--------------------------------------------------------------------------------

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        int height=FindHeight(root) ;
        vector<vector<int>> vec(height,vector<int> {});
        if(height==0)
            return vec ;
           
        int curr=0 ;
        queue<TreeNode*> que ;
        que.push(root) ;
       
        while(!que.empty()){
            int size=que.size() ;
            while(size--){
                TreeNode* temp ;
                temp=que.front() ;
                que.pop() ;
           
                vec[curr].push_back(temp->val);
               
                if(temp->left)
                    que.push(temp->left) ;
                if(temp->right)
                    que.push(temp->right) ;
            }
            curr++ ;
        }
        return vec ;
    }
   
    int FindHeight(TreeNode* root){
        if(root==NULL)
            return 0 ;
           
        int l=FindHeight(root->left) ;
        int r=FindHeight(root->right) ;
        return l>r?l+1:r+1 ;
    }
};

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