Create convert-sorted-list-to-binary-search-tree.cpp

Author: kamyu104

C++/convert-sorted-list-to-binary-search-tree.cpp

@@ -0,0 +1,47 @@
+// Time:  O(n)
+// Space: O(logn)
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    TreeNode* sortedListToBST(ListNode* head) {
+        auto curr = head;
+        int n = 0;
+        while (curr) {
+            curr = curr->next;
+            ++n;
+        }
+        return BuildBSTFromSortedDoublyListHelper(&head, 0, n);
+    }
+
+    TreeNode * BuildBSTFromSortedDoublyListHelper(ListNode **head, int s, int e) {
+        if (s == e) {
+            return nullptr;
+        }
+
+        int m = s + ((e - s) / 2);
+        auto left = BuildBSTFromSortedDoublyListHelper(head, s, m);
+        auto curr = new TreeNode((*head)->val);
+
+        *head = (*head)->next;
+        curr->left = left;
+        curr->right = BuildBSTFromSortedDoublyListHelper(head, m + 1, e);
+        return curr;
+    }
+};