feat: leetcode Construct Binary Search Tree from Preorder Traversal s…

leetcode/README.md

@@ -90,9 +90,10 @@
 | 938  | [Range Sum of BST](https://leetcode.com/problems/range-sum-of-bst/)                                                             | [C](./src/938.c)  | Easy       |
 | 965  | [Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree/)                                                   | [C](./src/965.c)  | Easy       |
 | 977  | [Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/)                                           | [C](./src/977.c)  | Easy       |
+| 1008 | [Construct Binary Search Tree from Preorder Traversal](https://leetcode.com/problems/construct-binary-search-tree-from-preorder-traversal/description/) | [C](./src/1008.c) | Medium |
 | 1019 | [Next Greater Node In Linked List](https://leetcode.com/problems/next-greater-node-in-linked-list/)                             | [C](./src/1019.c) | Medium     |
 | 1089 | [Duplicate Zeros](https://leetcode.com/problems/duplicate-zeros/)                                                               | [C](./src/1089.c) | Easy       |
 | 1184 | [Distance Between Bus Stops](https://leetcode.com/problems/distance-between-bus-stops/)                                         | [C](./src/1184.c) | Easy       |
 | 1189 | [Maximum Number of Balloons](https://leetcode.com/problems/maximum-number-of-balloons/)                                         | [C](./src/1189.c) | Easy       |
 | 1207 | [Unique Number of Occurrences](https://leetcode.com/problems/unique-number-of-occurrences/)                                     | [C](./src/1207.c) | Easy       |
-| 2130 | [Maximum Twin Sum of a Linked List](https://leetcode.com/problems/maximum-twin-sum-of-a-linked-list/)                           | [C](./src/2130.c) | Medium     |
+| 2130 | [Maximum Twin Sum of a Linked List](https://leetcode.com/problems/maximum-twin-sum-of-a-linked-list/)                           | [C](./src/2130.c) | Medium     |

leetcode/src/1008.c

@@ -0,0 +1,39 @@
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     struct TreeNode *left;
+ *     struct TreeNode *right;
+ * };
+ */
+
+struct TreeNode* bstFromPreorder(int* preorder, int preorderSize)
+{
+    struct TreeNode* new;
+    int left_ptr;
+
+    new = malloc(sizeof(struct TreeNode));
+    new->val = preorder[0];
+
+    if (preorderSize == 1)
+    {
+        new->right = NULL;
+        new->left = NULL;
+        return new;
+    }
+
+    left_ptr = 1;
+    while ((left_ptr < preorderSize) && (preorder[left_ptr] < preorder[0]))
+        left_ptr++;
+    if (left_ptr == 1)
+        new->left = NULL;
+    else
+        new->left = bstFromPreorder(preorder + 1, left_ptr - 1);
+    if (left_ptr < preorderSize)
+        new->right =
+            bstFromPreorder(preorder + left_ptr, preorderSize - left_ptr);
+    else
+        new->right = NULL;
+
+    return new;
+}