Question:

In a B+- tree where each node can hold at most four key values, a root to leaf path consists of the following nodes: 
\( A = (49, 77, 83, -) \) 
\( B = (7, 19, 33, 44) \) 
\( C = (20^*, 22^*, 25^*, 26^*) \) 
The *-marked keys signify that these are data entries in a leaf. Assume that a pointer between keys \( k_1 \) and \( k_2 \) points to a subtree containing keys in \([ k_1, k_2 )\), and that when a leaf is created, the smallest key in it is copied up into its parent. A record with key value 23 is inserted into the B+- tree. The smallest key value in the parent of the leaf that contains 25* is __________ . (Answer in integer)

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When inserting in a B+-tree, if a node overflows, it splits, and the smallest key of the new right node is pushed up.
Updated On: Apr 7, 2025
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Solution and Explanation

Step 1: Identify the Correct Leaf Node - Key 23 is inserted into leaf \( C \), which currently contains \( (20^*, 22^*, 25^*, 26^*) \). - After insertion, \( C \) will contain \( (20^*, 22^*, 23^*, 25^*, 26^*) \). 
Step 2: Leaf Node Splitting - Since each node can hold at most 4 keys, the leaf splits into two: - First leaf: \( (20^*, 22^*, 23^*) \) - Second leaf: \( (25^*, 26^*) \) - The smallest key of the second leaf (\( 25 \)) is pushed up into its parent (\( B \)). 
Step 3: Identify Parent Update - The updated keys in \( B \) are now \( (7, 19, 25, 33, 44) \). - Since \( B \) also exceeds the allowed 4 keys, it splits into two nodes: - First node: \( (7, 19) \) - Second node: \( (33, 44) \) - The smallest key of the second node (\( 33 \)) is pushed up into \( A \). Thus, the answer is \( 33 \).

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