day 9

Author: sachuverma

Leetcode Daily Challenge/February-2021/09. Convert BST to Greater Tree.cpp

@@ -0,0 +1,68 @@
+/*
+Convert BST to Greater Tree
+===========================
+
+Given the root of a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.
+
+As a reminder, a binary search tree is a tree that satisfies these constraints:
+
+The left subtree of a node contains only nodes with keys less than the node's key.
+The right subtree of a node contains only nodes with keys greater than the node's key.
+Both the left and right subtrees must also be binary search trees.
+Note: This question is the same as 1038: https://leetcode.com/problems/binary-search-tree-to-greater-sum-tree/
+
+Example 1:
+Input: root = [4,1,6,0,2,5,7,null,null,null,3,null,null,null,8]
+Output: [30,36,21,36,35,26,15,null,null,null,33,null,null,null,8]
+
+Example 2:
+Input: root = [0,null,1]
+Output: [1,null,1]
+
+Example 3:
+Input: root = [1,0,2]
+Output: [3,3,2]
+
+Example 4:
+Input: root = [3,2,4,1]
+Output: [7,9,4,10]
+
+Constraints:
+The number of nodes in the tree is in the range [0, 104].
+-104 <= Node.val <= 104
+All the values in the tree are unique.
+root is guaranteed to be a valid binary search tree.
+*/
+
+/**
+ * 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:
+  void rev_inorder(TreeNode *node, int &sum)
+  {
+    if (!node)
+      return;
+    rev_inorder(node->right, sum);
+    node->val += sum;
+    sum = node->val;
+    rev_inorder(node->left, sum);
+  }
+
+  TreeNode *convertBST(TreeNode *root)
+  {
+    int sum = 0;
+    rev_inorder(root, sum);
+    return root;
+  }
+};

Leetcode Daily Challenge/February-2021/README.MD

@@ -9,6 +9,7 @@
 | 5.  | [Simplify Path](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3629/) | [cpp](./05.%20Simplify%20Path.cpp) |
 | 6.  | [Binary Tree Right Side View](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3630/) | [cpp](./06.%20Binary%20Tree%20Right%20Side%20View.cpp) |
 | 7.  | [Shortest Distance to a Character](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/584/week-1-february-1st-february-7th/3631/) | [cpp](./07.%20Shortest%20Distance%20to%20a%20Character.cpp) | 
-| 8.  | [Peeking Iterator]() | [cpp](./08.%20Peeking%20Iterator.cpp) | 
+| 8.  | [Peeking Iterator](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3633/) | [cpp](./08.%20Peeking%20Iterator.cpp) | 
+| 9.  | [Convert BST to Greater Tree](https://leetcode.com/explore/challenge/card/february-leetcoding-challenge-2021/585/week-2-february-8th-february-14th/3634/) | [cpp](./09.%20Convert%20BST%20to%20Greater%20Tree.cpp) |