Added CPP code for Delete Node in a BST and Flatten Tree to Linked List

33. Flatten Binary Tree to Linked List.cpp

@@ -0,0 +1,86 @@
+/**
+ * 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 {
+    TreeNode* prev = NULL;
+
+public:
+    void flatten(TreeNode* root) {
+
+        /*
+        // Recursive Aproach:
+
+        if(root == NULL) return;
+
+        flatten(root->right);
+        flatten(root->left);
+
+        root->right = prev;
+        root->left = NULL;
+
+        prev = root;
+        */
+
+        /*
+        // Iterative Approach
+
+        if(root == NULL) return;
+
+        stack<TreeNode*> st;
+        st.push(root);
+
+        while(!st.empty()) {
+
+            TreeNode* curr = st.top();
+            st.pop();
+
+            if(curr->right) st.push(curr->right);
+            if(curr->left) st.push(curr->left);
+
+            if(st.empty() == false) {
+                curr->right = st.top();
+            }
+
+            curr->left = NULL;
+
+        }
+        */
+
+
+        // Morris Traversal Approach
+
+        if(root == NULL) return;
+
+        TreeNode* curr = root;
+
+        while(curr != NULL) {
+
+            if(curr->left) {
+                TreeNode* prev = curr->left;
+
+                while(prev->right) {
+                    prev = prev->right;
+                }
+
+                prev->right = curr->right;
+                curr->right = curr->left;
+                curr->left = NULL;
+
+            }
+
+            curr = curr->right;
+
+        }
+
+
+
+    }
+};

38. Delete Node in a BST.cpp

@@ -0,0 +1,63 @@
+/**
+ * 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 {
+private:
+    TreeNode* helper(TreeNode* root) {
+        if(root->left == NULL) { // no left subtree
+            return root->right;
+        }
+        else if(root->right == NULL) {  // no right subtree
+            return root->left;
+        }
+
+        TreeNode* rchild = root->right;
+        TreeNode* lastRightofLeft = findLastRight(root->left);
+        lastRightofLeft->right = rchild;
+
+        return root->left;
+    }
+
+    TreeNode* findLastRight(TreeNode* root) {
+        while(root->right != NULL) root = root->right;
+
+        return root;
+    }
+public:
+    TreeNode* deleteNode(TreeNode* root, int key) {
+        if(root == NULL) return NULL;
+        else if(key == root->val) {
+            return helper(root);
+        }
+
+        TreeNode* tmp = root;
+
+        while(root != NULL) {
+            if(root->val > key) {
+                if(root->left != NULL && root->left->val == key) {
+                    root->left = helper(root->left);
+                    break;
+                }
+                else root = root->left;
+            }
+
+            else {
+                if(root->right != NULL && root->right->val == key) {
+                    root->right = helper(root->right);
+                    break;
+                }
+                else root = root->right;
+            }
+        }
+
+        return tmp;
+    }
+};