solves pre order traversal in binary tree

Author: anishLearnsToCode

README.md

@@ -1,8 +1,8 @@
 # LeetCode Algorithms
 
-![problems-solved](https://img.shields.io/badge/Problems%20Solved-163/2081-1f425f.svg)
-![problems-solved-java](https://img.shields.io/badge/Java-163/2081-1abc9c.svg)
-![problems-solved-python](https://img.shields.io/badge/Python-163/2081-1abc9c.svg)
+![problems-solved](https://img.shields.io/badge/Problems%20Solved-165/2081-1f425f.svg)
+![problems-solved-java](https://img.shields.io/badge/Java-165/2081-1abc9c.svg)
+![problems-solved-python](https://img.shields.io/badge/Python-165/2081-1abc9c.svg)
 [![PRs Welcome](https://img.shields.io/badge/PRs-welcome-brightgreen.svg)](CONTRIBUTING.md)
 [![cp](https://img.shields.io/badge/also%20see-Competitve%20Programming-1f72ff.svg)](https://github.com/anishLearnsToCode/competitive-programming)
 
@@ -47,6 +47,7 @@
 | 125 | [Valid Palindrome](https://leetcode.com/problems/valid-palindrome) | [![Java](assets/java.png)](src/ValidPalindrome.java) [![Python](assets/python.png)](python/valid_palindrome.py) |
 | 136 | [Single Number](https://leetcode.com/problems/single-number) | [![Java](assets/java.png)](src/SingleNumber.java) [![Python](assets/python.png)](python/single_number.py) | 
 | 141 | [Linked List Cycle](https://leetcode.com/problems/linked-list-cycle) | [![Java](assets/java.png)](src/LinkedListCycle.java) [![Python](assets/python.png)](python/linked_list_cycle.py) | 
+| 144 | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/) | [![Java](assets/java.png)](src/BinaryTreePreOrderTraversal.java) [![Python](assets/python.png)](python/binary_tree_preorder_traversal.py) | 
 | 155 | [Min Stack](https://leetcode.com/problems/min-stack) | [![Java](assets/java.png)](src/MinStack.java) [![Python](assets/python.png)](python/min_stack.py) |
 | 157 | [Read N Characters Given Read4](https://leetcode.com/problems/read-n-characters-given-read4) | |
 | 160 | [Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists) | [![Java](assets/java.png)](src/IntersectionOf2LinkedLists.java) [![Python](assets/python.png)](python/intersecction_of_two_linked_lists.py) |

python/binary_tree_preorder_traversal.py

@@ -0,0 +1,22 @@
+# Definition for a binary tree node.
+from typing import Optional, List
+
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def _preorder_traversal(self, root: Optional[TreeNode], list: List[int]) -> None:
+        if root is None: return
+        list.append(root.val)
+        self._preorder_traversal(root.left, list)
+        self._preorder_traversal(root.right, list)
+
+    def preorderTraversal(self, root: Optional[TreeNode]) -> List[int]:
+        result = []
+        self._preorder_traversal(root, result)
+        return result

src/BinaryTreePreOrderTraversal.java

@@ -0,0 +1,17 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class BinaryTreePreOrderTraversal {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> result = new ArrayList<>();
+        preorderTraversal(root, result);
+        return result;
+    }
+
+    private void preorderTraversal(TreeNode root, List<Integer> list) {
+        if (root == null) return;
+        list.add(root.val);
+        preorderTraversal(root.left, list);
+        preorderTraversal(root.right, list);
+    }
+}