Adding leetcode solution recovering BST from preorder

Author: shashwat010

Tree/(LEETCODE)BST_from_preorderTraversal.cpp

@@ -0,0 +1,23 @@
+class Solution {
+public:
+    TreeNode* constructBST(vector<int> preorder,int low,int high){
+        if(low>=preorder.size() || low>high)
+        return NULL;
+
+        TreeNode* root=new TreeNode(preorder[low]);
+        if(high==low)
+        return root;
+        int i;
+        for(i=low;i<=high;i++)
+        if(preorder[i]>root->val)
+        break;
+
+        root->left=constructBST(preorder,low+1,i-1);
+        root->right=constructBST(preorder,i,high);
+        return root;
+    }
+
+    TreeNode* bstFromPreorder(vector<int>& preorder) {
+        return constructBST(preorder,0,preorder.size()-1);
+    }
+};