Create Optimized Approach.cpp

Author: JawadSher

18 - Binary Search Tree Data Structure Problems/16 - Construct Binary Search Tree from Pre-order Traversal/Optimized Approach.cpp

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+/**
+ * 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* solve(vector<int>& preorder, int maxi, int &i){
+        if(i >= preorder.size()) return NULL;
+
+        if(preorder[i] < 0 || preorder[i] > maxi) return NULL;
+
+        TreeNode* root = new TreeNode(preorder[i++]);
+        root -> left = solve(preorder, root -> val, i);
+        root -> right = solve(preorder, maxi, i);
+
+        return root;
+    }
+    TreeNode* bstFromPreorder(vector<int>& preorder) {
+        int maxi = INT_MAX;
+
+        int i = 0;
+        return solve(preorder, maxi, i);
+    }
+};