Trees & BSTs
Trees show up across SAP's interviews, usually at an easy to modest level. One SAP Concur software engineer had virtual technical rounds with a BST problem, a leaf count and a question about the nodes larger than a given leaf, and the advice they passed on afterwards was to brush up on trees. An SAP Labs Developer Associate round asked for plain BST search.
Rebuilding a tree from its preorder and inorder traversals is the toughest of these. A Java Developer Associate candidate got it in a first face-to-face technical round, between questions on OOP and Java threads, and walked through a brute force before the optimal build. In all three, say one thing out loud before you start coding. On the BST walk, explain why one comparison rules out a whole subtree, and on the leaf count, say what an empty tree returns. The rebuild needs a short explanation of why slicing arrays on every call drifts back to O(n²) on a skewed tree.
Settle the edges of the input before the recursion. An empty tree, a lone root, a target that is its own ancestor, and duplicate values that make two traversals ambiguous each change what the code returns. Each one takes a sentence to settle. SAP's tree rounds reward clarifying questions asked early, and getting these cases right decides whether the hidden tests pass.
SAPPremium lesson · Coding round
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