Merge pull request kothariji#515 from iamscoobydoo/master

(Leetcode)1008.Construct BST from Preorder

Author: kothariji

Tree/(LEETCODE)Construct_Binary_Search_Tree_from_Preorder_Traversal.cpp

@@ -0,0 +1,35 @@
+/**
+ * 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:
+    TreeNode* util(vector<int>& preorder, int* preIndex, int key, int min, int max, int size){
+        if(*preIndex >= size)
+            return NULL;
+        TreeNode* root = NULL;
+        if (key > min && key < max) {
+            root = new TreeNode(key);
+            *preIndex = *preIndex + 1;
+            if (*preIndex < size) {
+                root->left = util(preorder, preIndex, preorder[*preIndex], min, key, size);
+            }
+            if (*preIndex < size) {
+                root->right = util(preorder, preIndex, preorder[*preIndex], key, max, size);
+            }
+        }
+        return root;
+    }
+    
+    TreeNode* bstFromPreorder(vector<int>& preorder) {
+        int preIndex = 0;
+        return util(preorder, &preIndex, preorder[0], INT_MIN, INT_MAX, preorder.size());
+    }
+};