feat:add Solution.cpp for 0109.Convert Sorted List to Binary Search Tree

Author: Stackingrule

solution/0100-0199/0109.Convert Sorted List to Binary Search Tree/Solution.cpp

@@ -0,0 +1,19 @@
+class Solution {
+public:
+    TreeNode* sortedListToBST(ListNode* head) {
+        if (!head) return nullptr;
+        if (!head->next) return new TreeNode(head->val);
+        ListNode *fast = head, *slow = head, *last = slow;
+        while (fast->next && fast->next->next) {
+            last = slow;
+            slow = slow->next;
+            fast = fast->next->next;
+        }
+        fast = slow->next;
+        last->next = nullptr;
+        TreeNode *cur = new TreeNode(slow->val);
+        if (head != slow) cur->left = sortedListToBST(head);
+        cur->right = sortedListToBST(fast);
+        return cur; 
+    }
+};