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Author: elixered

1008-construct-binary-search-tree-from-preorder-traversal/1008-construct-binary-search-tree-from-preorder-traversal.cpp

@@ -0,0 +1,31 @@
+/**
+ * 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 s, int e)
+    {
+        if(s>e or e>preorder.size()) return NULL;
+        TreeNode* root = new TreeNode(preorder[s]);
+        if(s==e)
+            return root;
+        TreeNode *left=NULL,*right=NULL;
+        int idx = upper_bound(preorder.begin()+s,preorder.begin()+e+1,root->val) - preorder.begin();
+        left = solve(preorder,s+1,idx-1);
+        right = solve(preorder,idx,e);
+        root->left = left;
+        root->right = right;
+        return root;
+    }
+    TreeNode* bstFromPreorder(vector<int>& preorder) {
+        return solve(preorder,0,preorder.size()-1);
+    }
+};