14 may

Author: YuriSpiridonov

Challenges/2021/May-LeetCoding-Challenge.md

@@ -30,6 +30,7 @@ None
 |1423.|[Maximum Points You Can Obtain from Cards](https://leetcode.com/problems/maximum-points-you-can-obtain-from-cards/)|[Python](/Medium/1423.MaximumPointsYouCanObtainfromCards.py)|Medium|
 |304.|[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)|[Python](/Medium/304.RangeSumQuery2D-Immutable(bruteforce2).py)|Medium|
 |816.|[Ambiguous Coordinates](https://leetcode.com/problems/ambiguous-coordinates/)|~~Python~~|Medium|
+|114.|[PFlatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)|[Python](/Medium/114.FlattenBinaryTreetoLinkedList.py)|Medium|
 
 ## License
 The code is open-source and licensed under the [MIT License](/LICENSE).

Medium/114.FlattenBinaryTreetoLinkedList.py

@@ -0,0 +1,63 @@
+'''
+    Given the root of a binary tree, flatten the tree into 
+    a "linked list":
+        - The "linked list" should use the same TreeNode 
+          class where the right child pointer points to the 
+          next node in the list and the left child pointer 
+          is always null.
+        - The "linked list" should be in the same order as 
+          a pre-order traversal of the binary tree.
+
+    Example:
+    Input: root = [1,2,5,3,4,null,6]
+    Output: [1,null,2,null,3,null,4,null,5,null,6]
+
+    Example:
+    Input: root = []
+    Output: []
+
+    Example:
+    Input: root = [0]
+    Output: [0]
+
+    Constraints:
+        - The number of nodes in the tree is in the range 
+          [0, 2000].
+        - -100 <= Node.val <= 100
+    
+    Follow up: Can you flatten the tree in-place (with O(1) 
+               extra space)?
+'''
+#Difficulty: Medium
+#225 / 225 test cases passed.
+#Runtime: 40 ms
+#Memory Usage: 15.2 MB
+
+#Runtime: 40 ms, faster than 45.64% of Python3 online submissions for Flatten Binary Tree to Linked List.
+#Memory Usage: 15.2 MB, less than 45.95% of Python3 online submissions for Flatten Binary Tree to Linked List.
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+
+    def flatten(self, root: TreeNode) -> None:
+        """
+        Do not return anything, modify root in-place instead.
+        """
+        values = []
+        self.dfs(root, values)
+        for value in values[1:]:
+            root.right = TreeNode(value)
+            root.left = None
+            root = root.right
+
+    def dfs(self, root, values):
+        if not root:
+            return
+        values.append(root.val)
+        self.dfs(root.left, values)
+        self.dfs(root.right, values)

README.md

@@ -1,6 +1,6 @@
 # Python solutions of LeetCode problems.
 ![Language](https://img.shields.io/badge/language-Python-blue.svg) 
-![Problems Solved](https://img.shields.io/badge/problems%20solved-550%2F1665-orange) 
+![Problems Solved](https://img.shields.io/badge/problems%20solved-551%2F1665-orange) 
 [![License](https://img.shields.io/badge/license-MIT-green.svg)](./LICENSE) 
 ![Update](https://img.shields.io/badge/update-Daily-brightgreen.svg) 
 <br><br>
@@ -23,7 +23,7 @@ In this repository provided my Python solutions of LeetCode problems.
 - [February LeetCoding Challenge](/Challenges/2021/February-LeetCoding-Challenge.md) - 23/28
 - [March LeetCoding Challenge](/Challenges/2021/March-LeetCoding-Challenge.md) - 23/31
 - [April LeetCoding Challenge](/Challenges/2021/April-LeetCoding-Challenge.md) - 23/30
-- [May LeetCoding Challenge](/Challenges/2021/May-LeetCoding-Challenge.md) - 5/31
+- [May LeetCoding Challenge](/Challenges/2021/May-LeetCoding-Challenge.md) - 6/31
 <br><br>
 ## Solutions
 *P.S. If you like this, please leave me a star.* ★
@@ -106,6 +106,7 @@ In this repository provided my Python solutions of LeetCode problems.
 |110.|[Balanced Binary Tree](https://leetcode.com/problems/balanced-binary-tree/)|[Python](/Easy/110.BalancedBinaryTree.py)|Easy|`DFS`, `Recursion`|
 |111.|[Minimum Depth of Binary Tree](https://leetcode.com/problems/minimum-depth-of-binary-tree/)|[Python](/Easy/111.MinimumDepthofBinaryTree.py)|Easy|`Binary Tree`, `Recursion`|
 |112.|[Path Sum](https://leetcode.com/problems/path-sum/)|[Python](/Easy/112.PathSum.py)|Easy|`Binary Tree`, `Recursion`|
+|114.|[PFlatten Binary Tree to Linked List](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/)|[Python](/Medium/114.FlattenBinaryTreetoLinkedList.py)|Medium|`DFS`, preorder|
 |116.|[Populating Next Right Pointers in Each Node](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/)|[Python](/Medium/116.PopulatingNextRightPointersinEachNode.py)|Medium|`BFS`|
 |117.|[Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)|[Python](/Medium/117.PopulatingNextRightPointersinEachNodeII.py)|Medium|`BFS`, same as 116|
 |118.|[Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)|[Python](https://github.com/YuriSpiridonov/LeetCode/blob/master/Easy/118.PascalsTriangle.py)|Easy|