Create construct-binary-search-tree-from-preorder-traversal.cpp

Author: kamyu104

C++/construct-binary-search-tree-from-preorder-traversal.cpp

@@ -0,0 +1,40 @@
+// Time:  O(n)
+// Space: O(h)
+
+/**
+ * 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* bstFromPreorder(vector<int>& preorder) {
+        int index = 0;
+        return bstFromPreorderHelper(preorder,
+                                     numeric_limits<int>::min(),
+                                     numeric_limits<int>::max(),
+                                     &index);
+    }
+    
+private:
+    TreeNode* bstFromPreorderHelper(const vector<int>& preorder,
+                                    int left,
+                                    int right,
+                                    int *index) {
+
+        if (*index == preorder.size() ||
+            preorder[*index] < left ||
+            preorder[*index] > right) {
+            return nullptr;
+        }
+        
+        auto root = new TreeNode(preorder[(*index)++]);
+        root->left = bstFromPreorderHelper(preorder, left, root->val, index);
+        root->right = bstFromPreorderHelper(preorder, root->val, right, index);
+        return root;
+    }
+};