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‎README.md‎

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@@ -377,6 +377,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
377377

378378
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
379379
|-|-|-|-|-|-
380+
| 0121 |[Best Time to Buy and Sell Stock](src/main/scala/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 762 | 98.45
380381

381382
#### Day 8
382383

@@ -398,6 +399,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
398399

399400
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
400401
|-|-|-|-|-|-
402+
| 0096 |[Unique Binary Search Trees](src/main/scala/g0001_0100/s0096_unique_binary_search_trees/Solution.scala)| Medium | Top_100_Liked_Questions, Dynamic_Programming, Math, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(n)_Space_O(1) | 403 | 66.67
401403

402404
#### Day 12
403405

@@ -504,6 +506,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
504506

505507
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
506508
|-|-|-|-|-|-
509+
| 0104 |[Maximum Depth of Binary Tree](src/main/scala/g0101_0200/s0104_maximum_depth_of_binary_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(H) | 472 | 90.83
507510

508511
#### Day 11 Containers and Libraries
509512

@@ -771,11 +774,13 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
771774

772775
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
773776
|-|-|-|-|-|-
777+
| 0121 |[Best Time to Buy and Sell Stock](src/main/scala/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 762 | 98.45
774778

775779
#### Day 6 Tree
776780

777781
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
778782
|-|-|-|-|-|-
783+
| 0102 |[Binary Tree Level Order Traversal](src/main/scala/g0101_0200/s0102_binary_tree_level_order_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 522 | 83.33
779784

780785
#### Day 7 Binary Search
781786

@@ -786,6 +791,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
786791

787792
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
788793
|-|-|-|-|-|-
794+
| 0098 |[Validate Binary Search Tree](src/main/scala/g0001_0100/s0098_validate_binary_search_tree/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 507 | 70.21
789795

790796
#### Day 9 Graph/BFS/DFS
791797

@@ -906,6 +912,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
906912

907913
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
908914
|-|-|-|-|-|-
915+
| 0101 |[Symmetric Tree](src/main/scala/g0101_0200/s0101_symmetric_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 454 | 90.38
909916

910917
#### Day 16 Design
911918

@@ -961,6 +968,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
961968

962969
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
963970
|-|-|-|-|-|-
971+
| 0121 |[Best Time to Buy and Sell Stock](src/main/scala/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 762 | 98.45
964972
| 0001 |[Two Sum](src/main/scala/g0001_0100/s0001_two_sum/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Big_O_Time_O(n)_Space_O(n) | 517 | 86.66
965973
| 0055 |[Jump Game](src/main/scala/g0001_0100/s0055_jump_game/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Greedy, Big_O_Time_O(n)_Space_O(1) | 622 | 88.31
966974
| 0075 |[Sort Colors](src/main/scala/g0001_0100/s0075_sort_colors/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Sorting, Two_Pointers, Big_O_Time_O(n)_Space_O(1) | 450 | 84.21
@@ -997,6 +1005,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
9971005

9981006
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
9991007
|-|-|-|-|-|-
1008+
| 0114 |[Flatten Binary Tree to Linked List](src/main/scala/g0101_0200/s0114_flatten_binary_tree_to_linked_list/Solution.scala)| Medium | Top_100_Liked_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Linked_List, Big_O_Time_O(N)_Space_O(N) | 491 | 54.17
10001009
| 0024 |[Swap Nodes in Pairs](src/main/scala/g0001_0100/s0024_swap_nodes_in_pairs/Solution.scala)| Medium | Top_100_Liked_Questions, Linked_List, Recursion, Big_O_Time_O(n)_Space_O(1) | 441 | 95.65
10011010
| 0021 |[Merge Two Sorted Lists](src/main/scala/g0001_0100/s0021_merge_two_sorted_lists/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Linked_List, Recursion, Big_O_Time_O(m+n)_Space_O(m+n) | 480 | 89.72
10021011
| 0025 |[Reverse Nodes in k-Group](src/main/scala/g0001_0100/s0025_reverse_nodes_in_k_group/Solution.scala)| Hard | Top_100_Liked_Questions, Linked_List, Recursion, Big_O_Time_O(n)_Space_O(k) | 520 | 80.00
@@ -1005,6 +1014,11 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
10051014

10061015
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0094 |[Binary Tree Inorder Traversal](src/main/scala/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Big_O_Time_O(n)_Space_O(n) | 456 | 68.42
1018+
| 0102 |[Binary Tree Level Order Traversal](src/main/scala/g0101_0200/s0102_binary_tree_level_order_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 522 | 83.33
1019+
| 0104 |[Maximum Depth of Binary Tree](src/main/scala/g0101_0200/s0104_maximum_depth_of_binary_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(H) | 472 | 90.83
1020+
| 0124 |[Binary Tree Maximum Path Sum](src/main/scala/g0101_0200/s0124_binary_tree_maximum_path_sum/Solution.scala)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Dynamic_Programming, Depth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 523 | 89.47
1021+
| 0098 |[Validate Binary Search Tree](src/main/scala/g0001_0100/s0098_validate_binary_search_tree/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 507 | 70.21
10081022

10091023
#### Udemy Trie and Heap
10101024

@@ -1063,6 +1077,7 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
10631077

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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
1080+
| 0121 |[Best Time to Buy and Sell Stock](src/main/scala/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Big_O_Time_O(N)_Space_O(1) | 762 | 98.45
10661081

10671082
#### Day 4 Array
10681083

@@ -1101,11 +1116,15 @@ implementation 'com.github.javadev:leetcode-in-scala:1.0'
11011116

11021117
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0094 |[Binary Tree Inorder Traversal](src/main/scala/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Big_O_Time_O(n)_Space_O(n) | 456 | 68.42
11041120

11051121
#### Day 11 Tree
11061122

11071123
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0102 |[Binary Tree Level Order Traversal](src/main/scala/g0101_0200/s0102_binary_tree_level_order_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(N) | 522 | 83.33
1126+
| 0104 |[Maximum Depth of Binary Tree](src/main/scala/g0101_0200/s0104_maximum_depth_of_binary_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(H) | 472 | 90.83
1127+
| 0101 |[Symmetric Tree](src/main/scala/g0101_0200/s0101_symmetric_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 454 | 90.38
11091128

11101129
#### Day 12 Tree
11111130

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11211140

11221141
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0098 |[Validate Binary Search Tree](src/main/scala/g0001_0100/s0098_validate_binary_search_tree/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 507 | 70.21
11241144

11251145
### Data Structure II
11261146

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12071227

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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0105 |[Construct Binary Tree from Preorder and Inorder Traversal](src/main/scala/g0101_0200/s0105_construct_binary_tree_from_preorder_and_inorder_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Tree, Binary_Tree, Divide_and_Conquer, Big_O_Time_O(N)_Space_O(N) | 564 | 91.67
12101231

12111232
#### Day 16 Tree
12121233

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13201341

13211342
| # | Title | Difficulty | Tag | Time, ms | Time, %
13221343
|------|----------------|-------------|-------------|----------|---------
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| 0124 |[Binary Tree Maximum Path Sum](src/main/scala/g0101_0200/s0124_binary_tree_maximum_path_sum/Solution.scala)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Dynamic_Programming, Depth_First_Search, Tree, Binary_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(N)_Space_O(N) | 523 | 89.47
1345+
| 0121 |[Best Time to Buy and Sell Stock](src/main/scala/g0101_0200/s0121_best_time_to_buy_and_sell_stock/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Data_Structure_I_Day_3_Array, Dynamic_Programming_I_Day_7, Level_1_Day_5_Greedy, Udemy_Arrays, Big_O_Time_O(N)_Space_O(1) | 762 | 98.45
1346+
| 0114 |[Flatten Binary Tree to Linked List](src/main/scala/g0101_0200/s0114_flatten_binary_tree_to_linked_list/Solution.scala)| Medium | Top_100_Liked_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Linked_List, Udemy_Linked_List, Big_O_Time_O(N)_Space_O(N) | 491 | 54.17
1347+
| 0105 |[Construct Binary Tree from Preorder and Inorder Traversal](src/main/scala/g0101_0200/s0105_construct_binary_tree_from_preorder_and_inorder_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Tree, Binary_Tree, Divide_and_Conquer, Data_Structure_II_Day_15_Tree, Big_O_Time_O(N)_Space_O(N) | 564 | 91.67
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| 0104 |[Maximum Depth of Binary Tree](src/main/scala/g0101_0200/s0104_maximum_depth_of_binary_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Data_Structure_I_Day_11_Tree, Programming_Skills_I_Day_10_Linked_List_and_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(N)_Space_O(H) | 472 | 90.83
1349+
| 0102 |[Binary Tree Level Order Traversal](src/main/scala/g0101_0200/s0102_binary_tree_level_order_traversal/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Breadth_First_Search, Tree, Binary_Tree, Data_Structure_I_Day_11_Tree, Level_1_Day_6_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(N)_Space_O(N) | 522 | 83.33
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| 0101 |[Symmetric Tree](src/main/scala/g0101_0200/s0101_symmetric_tree/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Data_Structure_I_Day_11_Tree, Level_2_Day_15_Tree, Big_O_Time_O(N)_Space_O(log(N)) | 454 | 90.38
1351+
| 0098 |[Validate Binary Search Tree](src/main/scala/g0001_0100/s0098_validate_binary_search_tree/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree, Data_Structure_I_Day_14_Tree, Level_1_Day_8_Binary_Search_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(N)_Space_O(log(N)) | 507 | 70.21
1352+
| 0096 |[Unique Binary Search Trees](src/main/scala/g0001_0100/s0096_unique_binary_search_trees/Solution.scala)| Medium | Top_100_Liked_Questions, Dynamic_Programming, Math, Tree, Binary_Tree, Binary_Search_Tree, Dynamic_Programming_I_Day_11, Big_O_Time_O(n)_Space_O(1) | 403 | 66.67
1353+
| 0094 |[Binary Tree Inorder Traversal](src/main/scala/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.scala)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Stack, Data_Structure_I_Day_10_Tree, Udemy_Tree_Stack_Queue, Big_O_Time_O(n)_Space_O(n) | 456 | 68.42
13231354
| 0084 |[Largest Rectangle in Histogram](src/main/scala/g0001_0100/s0084_largest_rectangle_in_histogram/Solution.scala)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Array, Stack, Monotonic_Stack, Big_O_Time_O(n_log_n)_Space_O(log_n) | 904 | 71.43
13241355
| 0079 |[Word Search](src/main/scala/g0001_0100/s0079_word_search/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Matrix, Backtracking, Algorithm_II_Day_11_Recursion_Backtracking, Big_O_Time_O(4^(m\*n))_Space_O(m\*n) | 783 | 94.87
13251356
| 0078 |[Subsets](src/main/scala/g0001_0100/s0078_subsets/Solution.scala)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation, Backtracking, Algorithm_II_Day_9_Recursion_Backtracking, Udemy_Backtracking/Recursion, Big_O_Time_O(2^n)_Space_O(n\*2^n) | 452 | 87.50

‎src/main/scala/com_github_leetcode/TreeNode.scala‎

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package com_github_leetcode
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import scala.collection.mutable
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class TreeNode(var value: Int, var left: TreeNode = null, var right: TreeNode = null) {
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override def toString: String = {
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if (left == null && right == null) {
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value.toString
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} else {
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val root = value.toString
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val leftValue = Option(left).map(_.toString).getOrElse("null")
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val rightValue = Option(right).map(_.toString).getOrElse("null")
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s"$root,$leftValue,$rightValue"
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}
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}
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}
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object TreeNode {
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def create(treeValues: List[Option[Int]]): TreeNode = {
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if (treeValues.isEmpty) {
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null
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} else {
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val root = new TreeNode(treeValues.head.getOrElse(0))
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val queue = mutable.Queue(root)
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var i = 1
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while (i < treeValues.length) {
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val curr = queue.dequeue()
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if (treeValues(i).isDefined) {
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curr.left = new TreeNode(treeValues(i).get)
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queue.enqueue(curr.left)
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}
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i += 1
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if (i < treeValues.length && treeValues(i).isDefined) {
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curr.right = new TreeNode(treeValues(i).get)
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queue.enqueue(curr.right)
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}
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i += 1
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}
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root
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}
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}
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}

‎src/main/scala/g0001_0100/s0094_binary_tree_inorder_traversal/Solution.scala‎

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package g0001_0100.s0094_binary_tree_inorder_traversal
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// #Easy #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search #Tree #Binary_Tree
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// #Stack #Data_Structure_I_Day_10_Tree #Udemy_Tree_Stack_Queue #Big_O_Time_O(n)_Space_O(n)
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// #2023_11_03_Time_456_ms_(68.42%)_Space_57.3_MB_(7.89%)
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import com_github_leetcode.TreeNode
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import scala.collection.mutable.ListBuffer
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/*
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* Definition for a binary tree node.
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* class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
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* var value: Int = _value
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* var left: TreeNode = _left
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* var right: TreeNode = _right
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* }
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*/
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object Solution {
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def inorderTraversal(root: TreeNode): List[Int] = {
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if (root == null) {
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List.empty
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} else {
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val answer = ListBuffer[Int]()
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inorderTraversal(root, answer)
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answer.toList
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}
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}
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private def inorderTraversal(root: TreeNode, answer: ListBuffer[Int]): Unit = {
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if (root == null) {
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return
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}
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if (root.left != null) {
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inorderTraversal(root.left, answer)
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}
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answer += root.value
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if (root.right != null) {
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inorderTraversal(root.right, answer)
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}
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}
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}

‎src/main/scala/g0001_0100/s0094_binary_tree_inorder_traversal/readme.md‎

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94\. Binary Tree Inorder Traversal
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Easy
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Given the `root` of a binary tree, return _the inorder traversal of its nodes' values_.
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**Example 1:**
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![](https://assets.leetcode.com/uploads/2020/09/15/inorder_1.jpg)
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**Input:** root = [1,null,2,3]
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**Output:** [1,3,2]
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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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**Example 4:**
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![](https://assets.leetcode.com/uploads/2020/09/15/inorder_5.jpg)
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**Input:** root = [1,2]
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**Output:** [2,1]
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**Example 5:**
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![](https://assets.leetcode.com/uploads/2020/09/15/inorder_4.jpg)
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**Input:** root = [1,null,2]
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**Output:** [1,2]
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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?

‎src/main/scala/g0001_0100/s0096_unique_binary_search_trees/Solution.scala‎

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package g0001_0100.s0096_unique_binary_search_trees
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// #Medium #Top_100_Liked_Questions #Dynamic_Programming #Math #Tree #Binary_Tree
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// #Binary_Search_Tree #Dynamic_Programming_I_Day_11 #Big_O_Time_O(n)_Space_O(1)
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// #2023_11_03_Time_403_ms_(66.67%)_Space_51.5_MB_(100.00%)
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object Solution {
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def numTrees(n: Int): Int = {
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var result: Long = 1L
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for (i <- 0 until n) {
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result *= 2L * n - i
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result /= i + 1
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}
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result /= (n + 1)
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result.toInt
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}
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}

‎src/main/scala/g0001_0100/s0096_unique_binary_search_trees/readme.md‎

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96\. Unique Binary Search Trees
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Medium
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Given an integer `n`, return _the number of structurally unique **BST'**s (binary search trees) which has exactly_ `n` _nodes of unique values from_ `1` _to_ `n`.
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**Example 1:**
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![](https://assets.leetcode.com/uploads/2021/01/18/uniquebstn3.jpg)
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**Input:** n = 3
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**Output:** 5
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**Example 2:**
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**Input:** n = 1
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**Output:** 1
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**Constraints:**
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* `1 <= n <= 19`

‎src/main/scala/g0001_0100/s0098_validate_binary_search_tree/Solution.scala‎

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package g0001_0100.s0098_validate_binary_search_tree
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// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Depth_First_Search #Tree #Binary_Tree
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// #Binary_Search_Tree #Data_Structure_I_Day_14_Tree #Level_1_Day_8_Binary_Search_Tree
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// #Udemy_Tree_Stack_Queue #Big_O_Time_O(N)_Space_O(log(N))
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// #2023_11_03_Time_507_ms_(70.21%)_Space_57_MB_(93.62%)
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import com_github_leetcode.TreeNode
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/*
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* Definition for a binary tree node.
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* class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
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* var value: Int = _value
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* var left: TreeNode = _left
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* var right: TreeNode = _right
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* }
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*/
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object Solution {
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def isValidBST(root: TreeNode): Boolean = {
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def solve(node: TreeNode, left: Long, right: Long): Boolean = {
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if (node == null) {
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true
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} else if (node.value <= left || node.value >= right) {
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false
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} else {
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solve(node.left, left, node.value) && solve(node.right, node.value, right)
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}
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}
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solve(root, Long.MinValue, Long.MaxValue)
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}
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}

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