30 we came to know is the root of the tree . how did u come to know root of left subtree ?

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The preorder traversal sequence of a binary search tree is $30, 20, 10, 15, 25, 23, 39, 35, 42$. Which one of the following is the postorder traversal sequence of the same tree?

- $10, 20, 15, 23, 25, 35, 42, 39, 30$
- $15, 10, 25, 23, 20, 42, 35, 39, 30$
- $15, 20, 10, 23, 25, 42, 35, 39, 30$
- $15, 10, 23, 25, 20, 35, 42, 39, 30$

+30 votes

Best answer

Since it is a binary search tree, its inorder traversal produces a sorted sequence i.e. $\text{10, 15, 20, 23, 25, 30, 35, 39, 42}$.

Now given inorder and preorder traversals, we get following tree :

From this, we can give postorder traversal sequence as $\text{15,10,23,25,20,35,42,39,30}$ i.e. **option (D)**.

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