Create BST2.cpp

Author: TheSYNcoder

Topic/Solution/BST2.cpp

@@ -0,0 +1,54 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+/**
+ * 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:
+    ListNode* middle( ListNode* head){
+        ListNode* slow=head;
+        ListNode* fast =head;
+        ListNode* prev= NULL;
+        while( fast && fast->next){
+            prev = slow;
+            slow = slow->next;
+            fast = fast->next->next;
+        }
+        // slow is the mid
+        // when only head , prev is NULL
+        if ( prev)
+            prev->next=NULL;
+        return slow;
+    }
+        
+    
+    TreeNode* sortedListToBST(ListNode* head) {
+        
+        if (!head) return NULL;
+        // find middle 
+        ListNode* mid = middle( head);
+        TreeNode * node = new TreeNode( mid->val);
+        
+        if ( head == mid) return node;
+        node->left = sortedListToBST( head);
+        node->right = sortedListToBST(mid->next);
+        return node;
+        
+    }
+};