145. Binary Tree Postorder Traversal LeetCode Solution

In this guide, you will get 145. Binary Tree Postorder Traversal LeetCode Solution with the best time and space complexity. The solution to Binary Tree Postorder Traversal problem is provided in various programming languages like C++, Java, and Python. This will be helpful for you if you are preparing for placements, hackathons, interviews, or practice purposes. The solutions provided here are very easy to follow and include detailed explanations.

Table of Contents

1. Problem Statement
2. Complexity Analysis
3. Binary Tree Postorder Traversal solution in C++
4. Binary Tree Postorder Traversal solution in Java
5. Binary Tree Postorder Traversal solution in Python
6. Additional Resources

Problem Statement of Binary Tree Postorder Traversal

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

Example 1:

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

Example 2:

Input: root = [1,2,3,4,5,null,8,null,null,6,7,9]
Output: [4,6,7,5,2,9,8,3,1]
Explanation:

Example 3:

Input: root = []
Output: []

Example 4:

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

Constraints:

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

Follow up: Recursive solution is trivial, could you do it iteratively?

Complexity Analysis

• Time Complexity: O(n)
• Space Complexity: O(h)

145. Binary Tree Postorder Traversal LeetCode Solution in C++

class Solution {
 public:
  vector<int> postorderTraversal(TreeNode* root) {
    vector<int> ans;
    postorder(root, ans);
    return ans;
  }

 private:
  void postorder(TreeNode* root, vector<int>& ans) {
    if (root == nullptr)
      return;

    postorder(root->left, ans);
    postorder(root->right, ans);
    ans.push_back(root->val);
  }
};
/* code provided by PROGIEZ */

145. Binary Tree Postorder Traversal LeetCode Solution in Java

class Solution {
  public List<Integer> postorderTraversal(TreeNode root) {
    List<Integer> ans = new ArrayList<>();
    postorder(root, ans);
    return ans;
  }

  private void postorder(TreeNode root, List<Integer> ans) {
    if (root == null)
      return;

    postorder(root.left, ans);
    postorder(root.right, ans);
    ans.add(root.val);
  }
}
// code provided by PROGIEZ

145. Binary Tree Postorder Traversal LeetCode Solution in Python

class Solution:
  def postorderTraversal(self, root: TreeNode | None) -> list[int]:
    ans = []

    def postorder(root: TreeNode | None) -> None:
      if not root:
        return

      postorder(root.left)
      postorder(root.right)
      ans.append(root.val)

    postorder(root)
    return ans
 # code by PROGIEZ

Additional Resources

• Explore all LeetCode problem solutions at Progiez here
• Explore all problems on LeetCode website here

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