Sum Root to Leaf Numbers
A medium-tier problem at 69% community acceptance, tagged with Tree, Depth-First Search, Binary Tree. Reported in interviews at Meta and 2 others.
Sum Root to Leaf Numbers shows up at Meta, ServiceNow, and Visa with regularity, and it's the kind of problem that trips up candidates who haven't thought deeply about tree traversal. You're given a binary tree where each node contains a digit, and you need to treat each root-to-leaf path as a number, then sum them all. The acceptance rate sits at 68.5%, which means a third of people either miss the traversal pattern or botch the leaf detection. If this problem hits your live OA and the recursive framing doesn't click immediately, StealthCoder surfaces a working solution in seconds, invisible to the proctor.
Companies that ask "Sum Root to Leaf Numbers"
Sum Root to Leaf Numbers is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoderThe trap is conflating 'leaf' with 'node that exists'. Many candidates accumulate sums at every node, then get confused about when to actually count a path. The pattern: DFS down the tree, carry the number built so far (multiply by 10, add current node value), and only increment the result when you hit an actual leaf (no left and no right child). The recursion is cleaner than iterative because you can thread the accumulated number naturally through the call stack. Common fail: summing at internal nodes, forgetting to multiply by 10, or misidentifying leaf conditions. This is pure tree traversal wrapped in math notation, but the math part is trivial once the DFS is right. The topics here are Depth-First Search and Binary Tree fundamentals, so if you're shaky on how to walk a tree recursively, StealthCoder hedges that weakness on game day.
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Sum Root to Leaf Numbers recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Sum Root to Leaf Numbers interview FAQ
Is this really a medium difficulty problem at Meta?+
Yes. The 68.5% acceptance rate confirms it's legitimately medium, not an easy win. The trick isn't the math (multiplying by 10 and adding digits), it's correctly identifying leaf nodes during DFS. Most mistakes happen there, not in the summation logic.
What's the difference between an internal node and a leaf in this context?+
A leaf has both left and right pointers as null. Internal nodes have at least one child. You only count the number when you hit a leaf. Checking this condition incorrectly is the #1 bug.
Should I build the number iteratively or during recursion?+
Build it during recursion. Pass the accumulated number as a parameter: new_number = current_number * 10 + node.val. When you hit a leaf, add that number to your result. It's cleaner and avoids off-by-one errors.
Does this problem test anything beyond tree traversal?+
Not really. It's a DFS warmup with digit arithmetic bolted on. If you're solid on recursive tree walking, the problem is straightforward. It's medium because people rush and skip the leaf-detection logic.
How does this relate to other binary tree problems at FAANG?+
It's a sibling to problems like Path Sum and Binary Tree Paths. All three test DFS correctness and recursive thinking. This one adds the 'accumulate state as you traverse' pattern, which appears frequently in medium-level tree assessments.
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