104 lines
1.8 KiB
Markdown
104 lines
1.8 KiB
Markdown
# Leetcode Binary-Tree-Postorder-Traversal
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#### 2022-07-04 21:31
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> ##### Algorithms:
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>
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> #algorithm #DFS #DFS_postorder
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>
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> ##### Data structures:
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>
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> #DS #binary_tree
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>
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> ##### Difficulty:
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>
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> #coding*problem #difficulty*
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>
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> ##### Additional tags:
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>
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> #leetcode #CS_list_need_practicing
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>
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> ##### Revisions:
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>
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> N/A
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##### Related topics:
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##### Links:
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- [Link to problem](https://leetcode.com/problems/binary-tree-postorder-traversal/)
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---
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### Problem
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https://leetcode.com/problems/binary-tree-postorder-traversal/
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#### Examples
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**Example 1:**
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**Input:** root = [1,null,2,3]
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**Output:** [3,2,1]
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**Example 2:**
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**Input:** root = []
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**Output:** []
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**Example 3:**
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**Input:** root = [1]
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**Output:** [1]
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#### Constraints
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- The number of the nodes in the tree is in the range `[0, 100]`.
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- `-100 <= Node.val <= 100`
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### Thoughts
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Same as [[Leetcode Binary-Tree-Inorder-Traversal]] and [[Leetcode Binary-Tree-Preorder-Traversal]]
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== TODO: write iteration and another algo #TODO ==
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### Solution
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Recursion
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```cpp
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/**
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* Definition for a binary tree node.
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* struct TreeNode {
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* int val;
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* TreeNode *left;
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* TreeNode *right;
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* TreeNode() : val(0), left(nullptr), right(nullptr) {}
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* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
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* right(right) {}
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* };
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*/
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class Solution {
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void postorder(TreeNode *root, vector<int> &answer) {
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if (root == nullptr) {
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return;
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}
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postorder(root->left, answer);
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postorder(root->right, answer);
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answer.push_back(root->val);
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}
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public:
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vector<int> postorderTraversal(TreeNode *root) {
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vector<int> answer;
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postorder(root, answer);
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return answer;
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}
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};
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```
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