post-order-traversal

Problem Description

Given the root of a binary tree, return the postorder traversal of its nodes' values.

Examples

Example 1:

Input: root = [1,null,2,3]
Output: [1,2,3]

Example 2:

Input: root = []
Output: []

Example 3:

Input: root = [1]
Output: [1]

Constraints

• The number of nodes in the tree is in the range [0, 100].
• -1000 <= Node.val <= 1000

Solution for Binary Tree Post Order Traversal

Intuition

• Recursive is very easy try with iterative way

Code in Different Languages

Python

Written by @parikhitkurmi

//python
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
 def postorderTraversal(self, root):
     """
     :type root: TreeNode
     :rtype: List[int]
     """
     stack=[]
     def dfs(root):
         if root:
             dfs(root.left)
             dfs(root.right)
             stack.append(root.val)
     dfs(root)
     return stack   
     

Java

Written by @parikhitkurmi

//java

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode() {}
*     TreeNode(int val) { this.val = val; }
*     TreeNode(int val, TreeNode left, TreeNode right) {
*         this.val = val;
*         this.left = left;
*         this.right = right;
*     }
* }
*/
class Solution {
 ArrayList<Integer> res = new ArrayList<>();
 public List<Integer> postorderTraversal(TreeNode root) {
     postOrder(root);
     return res;
 }

 private void postOrder(TreeNode root){
     if(root == null){
         return;
     }
     postOrder(root.left);
     postOrder(root.right);
     res.add(root.val);
 }
}

C++

Written by @parikhitkurmi

//cpp

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode() : val(0), left(nullptr), right(nullptr) {}
*     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
*     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:

  vector<int> ans ;
  void postorder(TreeNode* root) 
  {
     if(!root) 
     return ;

     postorder(root->left) ;
     postorder(root->right) ;

     ans.push_back(root->val) ;
     

  } 
 vector<int> postorderTraversal(TreeNode* root) {

     postorder(root) ;
     return ans ;
     
 }
};

References

• LeetCode Problem: Binary Tree Inorder Traversal
• Solution Link: Binary Tree Inorder Traversal
• Authors GeeksforGeeks Profile: parikhit kurmi
• Authors Leetcode: parikhit kurmi