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solved 144. Binary Tree Preorder Traversal
Signed-off-by: rajput-hemant <[email protected]>
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‎TOPICWISE.md‎

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| **0104** | [Maximum Depth of Binary Tree][104] | Tree, BFS, DFS, Binary Tree | ![][easy] | |
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| **0110** | [Balanced Binary Tree][110] | Tree, DFS, Binary Tree | ![][easy] | |
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| **0111** | [Minimum Depth of Binary Tree][111] | Tree, DFS, BFS, Binary Tree | ![][easy] | |
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| **0144** | [Binary Tree Preorder Traversal][144] | Stack, Tree, DFS, Binary Tree | ![][easy] | |
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| **0199** | [Binary Tree Right Side View][199] | Tree, DFS, BFS, Binary Tree | ![][medium] | |
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| **0222** | [Count Complete Tree Nodes][222] | Binary Search, Tree, DFS, Binary Tree | ![][medium] | |
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| **0230** | [Kth Smallest Element in a BST ][230] | Tree, DFS, BST, Binary Tree | ![][medium] | |
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| **0104** | [Maximum Depth of Binary Tree][104] | Tree, BFS, DFS, Binary Tree | ![][easy] | |
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| **0110** | [Balanced Binary Tree][110] | Tree, DFS, Binary Tree | ![][easy] | |
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| **0111** | [Minimum Depth of Binary Tree][111] | Tree, DFS, BFS, Binary Tree | ![][easy] | |
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| **0144** | [Binary Tree Preorder Traversal][144] | Stack, Tree, DFS, Binary Tree | ![][easy] | |
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| **0199** | [Binary Tree Right Side View][199] | Tree, DFS, BFS, Binary Tree | ![][medium] | |
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| **0222** | [Count Complete Tree Nodes][222] | Binary Search, Tree, DFS, Binary Tree | ![][medium] | |
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| **0230** | [Kth Smallest Element in a BST ][230] | Tree, DFS, BST, Binary Tree | ![][medium] | |
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| **0104** | [Maximum Depth of Binary Tree][104] | Tree, BFS, DFS, Binary Tree | ![][easy] | |
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| **0110** | [Balanced Binary Tree][110] | Tree, DFS, Binary Tree | ![][easy] | |
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| **0111** | [Minimum Depth of Binary Tree][111] | Tree, DFS, BFS, Binary Tree | ![][easy] | |
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| **0144** | [Binary Tree Preorder Traversal][144] | Stack, Tree, DFS, Binary Tree | ![][easy] | |
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| **0199** | [Binary Tree Right Side View][199] | Tree, DFS, BFS, Binary Tree | ![][medium] | |
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| **0222** | [Count Complete Tree Nodes][222] | Binary Search, Tree, DFS, Binary Tree | ![][medium] | |
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| **0230** | [Kth Smallest Element in a BST ][230] | Tree, DFS, BST, Binary Tree | ![][medium] | |
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| # | Solution | Tags | Difficulty | Remark |
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| :------: | :----------------------------------------------: | :---------------------------: | :--------: | :----: |
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| **0094** | [Binary Tree Inorder Traversal][94] | Tree, Stack, DFS, Binary Tree | ![][easy] | |
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| **0144** | [Binary Tree Preorder Traversal][144] | Stack, Tree, DFS, Binary Tree | ![][easy] | |
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| **1047** | [Remove All Adjacent Duplicates In String][1047] | String, Stack | ![][easy] | |
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<!--
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[104]: ./src/0101-0200/104%20-%20Maximum%20Depth%20of%20Binary%20Tree/
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[110]: ./src/0101-0200/110%20-%20Balanced%20Binary%20Tree/
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[111]: ./src/0101-0200/111%20-%20Minimum%20Depth%20of%20Binary%20Tree/
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[144]: ./src/0101-0200/144%20-%20Binary%20Tree%20Preorder%20Traversal/
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[172]: ./src/0101-0200/172%20-%20Factorial%20Trailing%20Zeroes/
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[199]: ./src/0101-0200/199%20-%20Binary%20Tree%20Right%20Side%20View/
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[222]: ./src/0201-0300/222%20-%20Count%20Complete%20Tree%20Nodes/

‎src/0101-0200/144 - Binary Tree Preorder Traversal/BinaryTreePreorderTraversal.java‎

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import java.util.ArrayList;
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import java.util.List;
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import java.util.Stack;
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import definitions.TreeNode;
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public class BinaryTreePreorderTraversal {
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List<Integer> list = new ArrayList<Integer>();
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// Iterative Approach
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public List<Integer> preorderTraversal(TreeNode root) {
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if (root == null)
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return list;
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Stack<TreeNode> stack = new Stack<>();
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stack.push(root);
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while (!stack.isEmpty()) {
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TreeNode current = stack.pop();
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list.add(current.val);
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if (current.right != null)
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stack.push(current.right);
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if (current.left != null)
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stack.push(current.left);
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}
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return list;
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}
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// Recursive Approach
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public List<Integer> preorderTraversalRecursive(TreeNode root) {
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if (root != null) {
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list.add(root.val);
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preorderTraversalRecursive(root.left);
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preorderTraversalRecursive(root.right);
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}
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return list;
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}
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}

‎src/0101-0200/144 - Binary Tree Preorder Traversal/README.md‎

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# 144. Binary Tree Preorder Traversal [![share]](https://leetcode.com/problems/binary-tree-preorder-traversal/submissions)
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![][easy]
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## Problem Statement:
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Given the `root` of a binary tree, return the preorder traversal of its nodes' values.
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![](https://assets.leetcode.com/uploads/2020/09/15/inorder_1.jpg)
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### Example 1:
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```
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Input: root = [1,null,2,3]
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Output: [1,2,3]
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```
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### Example 2:
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```
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Input: root = []
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Output: []
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```
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### Example 3:
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```
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Input: root = [1]
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Output: [1]
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```
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### Constraints:
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The number of nodes in the tree is in the range [0, 100].
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-100 <= Node.val <= 100
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Follow up: Recursive solution is trivial, could you do it iteratively?
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## Solution:
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### [_Java_]()
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```java
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List<Integer> list = new ArrayList<Integer>();
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// Iterative Approach
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public List<Integer> preorderTraversal(TreeNode root) {
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if (root == null)
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return list;
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Stack<TreeNode> stack = new Stack<>();
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stack.push(root);
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while (!stack.isEmpty()) {
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TreeNode current = stack.pop();
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list.add(current.val);
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if (current.right != null)
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stack.push(current.right);
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if (current.left != null)
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stack.push(current.left);
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}
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return list;
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}
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// Recursive Approach
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public List<Integer> preorderTraversalRecursive(TreeNode root) {
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if (root != null) {
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list.add(root.val);
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preorderTraversalRecursive(root.left);
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preorderTraversalRecursive(root.right);
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}
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return list;
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}
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```
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### [_..._]()
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```
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```
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<!----------------------------------{ link }--------------------------------->
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[share]: https://img.icons8.com/external-anggara-blue-anggara-putra/20/000000/external-share-user-interface-basic-anggara-blue-anggara-putra-2.png
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[easy]: https://img.shields.io/badge/Difficulty-Easy-bright.svg
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[medium]: https://img.shields.io/badge/Difficulty-Medium-yellow.svg
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[hard]: https://img.shields.io/badge/Difficulty-Hard-red.svg

‎src/README.md‎

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| **0104** | [Maximum Depth of Binary Tree][104] | Tree, BFS, DFS, Binary Tree | ![][easy] | |
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| **0110** | [Balanced Binary Tree][110] | Tree, DFS, Binary Tree | ![][easy] | |
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| **0111** | [Minimum Depth of Binary Tree][111] | Tree, DFS, BFS, Binary Tree | ![][easy] | |
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| **0144** | [Binary Tree Preorder Traversal][144] | Stack, Tree, DFS, Binary Tree | ![][easy] | |
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| **0172** | [Factorial Trailing Zeroes][172] | Math | ![][medium] | |
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| **0199** | [Binary Tree Right Side View][199] | Tree, DFS, BFS, Binary Tree | ![][medium] | |
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| **0222** | [Count Complete Tree Nodes][222] | Binary Search, Tree, DFS, Binary Tree | ![][medium] | |
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[104]: ./0101-0200/104%20-%20Maximum%20Depth%20of%20Binary%20Tree/
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[110]: ./0101-0200/110%20-%20Balanced%20Binary%20Tree/
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[111]: ./0101-0200/111%20-%20Minimum%20Depth%20of%20Binary%20Tree/
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[144]: ./0101-0200/144%20-%20Binary%20Tree%20Preorder%20Traversal/
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[172]: ./0101-0200/172%20-%20Factorial%20Trailing%20Zeroes/
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[199]: ./0101-0200/199%20-%20Binary%20Tree%20Right%20Side%20View/
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[222]: ./0201-0300/222%20-%20Count%20Complete%20Tree%20Nodes/

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