Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 26

Description

N-ary Tree Postorder Traversal

Given the root of an n-ary tree, return the postorder traversal of its nodes' values.

Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

Example 1:

Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]

Example 2:

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]

Constraints:

• The number of nodes in the tree is in the range [0, 104].
• 0 <= Node.val <= 104
• The height of the n-ary tree is less than or equal to 1000.

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

Solution

class Solution {
  void visit(vector<int> &answer, Node* root) {
    for(auto child : root->children) {
      visit(answer, child);
    }
    answer.push_back(root->val);
  }
public:
  vector<int> postorder(Node* root) {
    if(!root) return {};
    vector<int> answer;
    visit(answer, root);
    return answer;
  }
};