vault backup: 2022-07-08 11:29:47

.obsidian/graph.json

@@ -32,6 +32,6 @@
   "repelStrength": 10,
   "linkStrength": 1,
   "linkDistance": 250,
-  "scale": 0.8153718570546582,
+  "scale": 0.8153718570546572,
   "close": true
 }

OJ notes/OJ-index.md

@@ -34,6 +34,7 @@ tag:#CS_list_need_practicing
  
 - [ ] [[Leetcode Binary-Tree-Postorder-Traversal]]
 - [ ] [[Leetcode Reverse-Linked-List]]
+- [ ] [[Leetcode Validate-Binary-Search-Tree]]
  
 
 
@@ -54,7 +55,9 @@ tag:#leetcode
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
 - [[Leetcode First-Unique-Character-In-a-String]]
 - [[Leetcode Implement-Queue-Using-Stacks]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Intersection-of-Two-Arrays-II]]
+- [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Linked-List-Cycle]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Maximum-Difference-Between-Increasing-Elements]]
@@ -62,16 +65,20 @@ tag:#leetcode
 - [[Leetcode Merge-Sorted-Array]]
 - [[Leetcode Merge-Two-Sorted-Lists]]
 - [[Leetcode Pascal's-Triangle]]
+- [[Leetcode Path-Sum]]
 - [[Leetcode Ransom-Note]]
 - [[Leetcode Remove-Duplicates-From-Sorted-List]]
 - [[Leetcode Remove-Linked-List-Elements]]
 - [[Leetcode Reshape-The-Matrix]]
 - [[Leetcode Reverse-Linked-List]]
 - [[Leetcode Search-a-2D-Matrix]]
+- [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
 - [[Leetcode Two-Sum]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
 - [[Leetcode Valid-Anagram]]
 - [[Leetcode Valid-Sudoku]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
  
@@ -103,23 +110,29 @@ tag:#DS tag:#coding_problem -tag:#template_remove_me
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
 - [[Leetcode First-Unique-Character-In-a-String]]
 - [[Leetcode Implement-Queue-Using-Stacks]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Intersection-of-Two-Arrays-II]]
+- [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Linked-List-Cycle]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Maxinum-subarray]]
 - [[Leetcode Merge-Sorted-Array]]
 - [[Leetcode Merge-Two-Sorted-Lists]]
 - [[Leetcode Pascal's-Triangle]]
+- [[Leetcode Path-Sum]]
 - [[Leetcode Ransom-Note]]
 - [[Leetcode Remove-Duplicates-From-Sorted-List]]
 - [[Leetcode Remove-Linked-List-Elements]]
 - [[Leetcode Reshape-The-Matrix]]
 - [[Leetcode Reverse-Linked-List]]
 - [[Leetcode Search-a-2D-Matrix]]
+- [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
 - [[Leetcode Two-Sum]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
 - [[Leetcode Valid-Anagram]]
 - [[Leetcode Valid-Sudoku]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
  
@@ -129,6 +142,7 @@ tag:#DS tag:#CS_analysis -tag:#template_remove_me
 - [[$filename]]
 ```
  
+- [[Breadth First Search]]
 - [[cpp_Range_based_for_loop]]
 - [[cpp_std_multiset]]
 - [[cpp_std_unordered_map]]
@@ -149,7 +163,9 @@ tag:#algorithm tag:#coding_problem -tag:#template_remove_me
 - [[Leetcode Binary-Tree-Postorder-Traversal]]
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
 - [[Leetcode First-Unique-Character-In-a-String]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Intersection-of-Two-Arrays-II]]
+- [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Linked-List-Cycle]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Maximum-Difference-Between-Increasing-Elements]]
@@ -157,12 +173,16 @@ tag:#algorithm tag:#coding_problem -tag:#template_remove_me
 - [[Leetcode Merge-Sorted-Array]]
 - [[Leetcode Merge-Two-Sorted-Lists]]
 - [[Leetcode Pascal's-Triangle]]
+- [[Leetcode Path-Sum]]
 - [[Leetcode Ransom-Note]]
 - [[Leetcode Reverse-Linked-List]]
 - [[Leetcode Search-a-2D-Matrix]]
+- [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
 - [[Leetcode Two-Sum]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
 - [[Leetcode Valid-Anagram]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 
@@ -176,6 +196,7 @@ tag:#algorithm tag:#CS_analysis -tag:#template_remove_me
 ```
  
 - [[Binary Search Algorithm]]
+- [[Breadth First Search]]
 - [[cpp_std_sort]]
 - [[Floyd's Cycle Finding Algorithm]]
 - [[Kadane's Algorithm]]

OJ notes/pages/Breadth First Search.md

@@ -0,0 +1,41 @@
+# Breadth First Search
+
+#### 2022-07-08 11:19
+
+> ##### Algorithms:
+> #algorithm #BFS 
+> ##### Data structures:
+> #DS #binary_tree 
+> ##### Difficulty:
+> #CS_analysis #difficulty-
+> ##### Additional tags:
+> 
+
+##### Related problems:
+```expander
+tag:#coding_problem tag:#BFS -tag:#template_remove_me 
+```
+ 
+- [[Leetcode Binary-Tree-Level-Order-Traversal]]
+- [[Leetcode Maximum-Depth-Of-Binary-Tree]]
+- [[Leetcode Search-In-a-Binary-Tree]]
+- [[Leetcode Symmetric-Tree]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
+ 
+
+##### Links:
+- [cppreference]()
+___
+
+### What is Breadth First Search?
+means BFS
+
+### How does Breadth First Search work?
+
+#### Example code
+
+### Why and when to use it?
+
+> [!tip] Whether to push root or root's nodes initially
+> When checking the symmetry, [[Leetcode Symmetric-Tree]], push nodes to make sure the stack can be poped correctly.
+> otherwise, check if the root node is needed and minimum amount of nodes in the tree is larger than 1

OJ notes/pages/Leetcode Binary-Tree-Inorder-Traversal.md

@@ -20,11 +20,13 @@ tag:#DFS
  
 - [[Leetcode Binary-Tree-Postorder-Traversal]]
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Path-Sum]]
 - [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Binary-Tree-Level-Order-Traversal.md

@@ -20,6 +20,8 @@ tag:#BFS
  
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Search-In-a-Binary-Tree]]
+- [[Leetcode Symmetric-Tree]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Binary-Tree-Postorder-Traversal.md

@@ -20,11 +20,13 @@ tag:#DFS
  
 - [[Leetcode Binary-Tree-Inorder-Traversal]]
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Path-Sum]]
 - [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Binary-Tree-Preorder-Traversal.md

@@ -20,11 +20,13 @@ tag:#DFS
  
 - [[Leetcode Binary-Tree-Inorder-Traversal]]
 - [[Leetcode Binary-Tree-Postorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Path-Sum]]
 - [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Insert-Into-a-Binary-Search-Tree.md

@@ -26,6 +26,7 @@ tag:#DFS
 - [[Leetcode Path-Sum]]
 - [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Maximum-Depth-Of-Binary-Tree.md

@@ -20,6 +20,8 @@ tag:#BFS
  
 - [[Leetcode Binary-Tree-Level-Order-Traversal]]
 - [[Leetcode Search-In-a-Binary-Tree]]
+- [[Leetcode Symmetric-Tree]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Path-Sum.md

@@ -21,10 +21,12 @@ tag:#DFS
 - [[Leetcode Binary-Tree-Inorder-Traversal]]
 - [[Leetcode Binary-Tree-Postorder-Traversal]]
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Search-In-a-Binary-Tree]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Search-In-a-Binary-Tree.md

@@ -22,10 +22,13 @@ tag:#DFS OR tag:#BFS
 - [[Leetcode Binary-Tree-Level-Order-Traversal]]
 - [[Leetcode Binary-Tree-Postorder-Traversal]]
 - [[Leetcode Binary-Tree-Preorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
 - [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
 - [[Leetcode Path-Sum]]
 - [[Leetcode Symmetric-Tree]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:

OJ notes/pages/Leetcode Symmetric-Tree.md

@@ -3,7 +3,7 @@
 #### 2022-07-05 10:15
 
 > ##### Algorithms:
-> #algorithm #DFS #recursion 
+> #algorithm #DFS #recursion #BFS 
 > ##### Data structures:
 > #DS #binary_tree 
 > ##### Difficulty:
@@ -15,11 +15,20 @@
 
 ##### Related topics:
 ```expander
-tag:#DFS or tag:#BFS
+tag:#DFS OR tag:#BFS
 ```
  
+- [[Leetcode Binary-Tree-Inorder-Traversal]]
+- [[Leetcode Binary-Tree-Level-Order-Traversal]]
+- [[Leetcode Binary-Tree-Postorder-Traversal]]
+- [[Leetcode Binary-Tree-Preorder-Traversal]]
+- [[Leetcode Insert-Into-a-Binary-Search-Tree]]
+- [[Leetcode Invert-Binary-Tree]]
 - [[Leetcode Maximum-Depth-Of-Binary-Tree]]
+- [[Leetcode Path-Sum]]
 - [[Leetcode Search-In-a-Binary-Tree]]
+- [[Leetcode Two-Sum-IV-Input-Is-a-BST]]
+- [[Leetcode Validate-Binary-Search-Tree]]
  
 
 ##### Links:
@@ -111,7 +120,7 @@ public:
 };
 ```
 
-Iteration, 8ms
+BFS, iteration, 8ms
 ```cpp
 /**
  * Definition for a binary tree node.

OJ notes/pages/Leetcode Two-Sum-IV-Input-Is-a-BST.md

@@ -0,0 +1,117 @@
+# Leetcode Two-Sum-IV-Input-Is-a-BST
+
+#### 2022-07-08 11:11
+
+> ##### Algorithms:
+> #algorithm #binary_search #BFS 
+> ##### Data structures:
+> #DS #binary_tree #binary_search_tree 
+> ##### Difficulty:
+> #coding_problem #difficulty-easy
+> ##### Additional tags:
+> #leetcode
+> ##### Revisions:
+> N/A
+
+##### Related topics:
+```expander
+tag:#BFS OR tag:#binary_search
+```
+ 
+- [[Binary Search Algorithm]]
+- [[Leetcode Binary-Tree-Level-Order-Traversal]]
+- [[Leetcode Maximum-Depth-Of-Binary-Tree]]
+- [[Leetcode Search-a-2D-Matrix]]
+- [[Leetcode Search-In-a-Binary-Tree]]
+- [[Leetcode Symmetric-Tree]]
+ 
+
+##### Links:
+- [Link to problem](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/)
+- [Three method to solve this](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/discuss/106059/JavaC%2B%2B-Three-simple-methods-choose-one-you-like)
+___
+### Problem
+
+Given the `root` of a Binary Search Tree and a target number `k`, return _`true` if there exist two elements in the BST such that their sum is equal to the given target_.
+
+#### Examples
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/09/21/sum_tree_1.jpg)
+
+**Input:** root = [5,3,6,2,4,null,7], k = 9
+**Output:** true
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2020/09/21/sum_tree_2.jpg)
+
+**Input:** root = [5,3,6,2,4,null,7], k = 28
+**Output:** false
+
+#### Constraints
+
+-   The number of nodes in the tree is in the range `[1, 104]`.
+-   `-104 <= Node.val <= 104`
+-   `root` is guaranteed to be a **valid** binary search tree.
+-   `-105 <= k <= 105`
+
+### Thoughts
+
+> [!summary]
+> This is a #BFS #hash_table problem.
+
+Mainly two methods:
+1. #BFS with hash table. Time space O(n)
+	This can be quicker since you are starting at the middle, which is more likely to hit the answer, theoretically taking less time.
+2. #binary_search. Time O(hn), h is the height of BST, best case h == log(n), worst case h == n
+	for every node, binary search in the tree for the answer.
+
+### Solution
+
+BFS with hash table
+```cpp
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+  bool findTarget(TreeNode* root, int k) {
+    // BFS with unordered_set
+    // Take note: when to push root, when to push root->left and root->right
+    unordered_set<int> uset;
+    queue<TreeNode*> pending;
+    pending.push(root);
+    
+    TreeNode* ptr;
+    while(!pending.empty()) {
+      ptr = pending.front();
+      pending.pop();
+      
+      // find first, to avoid k = 10, val = 5
+      if (uset.find(ptr->val) != uset.end()) {
+        return true;
+      }
+      uset.insert(k - ptr->val);
+      
+      if (ptr->left) {
+        pending.push(ptr->left);
+      }
+      if (ptr->right) {
+        pending.push(ptr->right);
+      }
+    }
+    
+    return false;
+  }
+};
+```