Minimum Depth of Binary Tree
A easy-tier problem at 51% community acceptance, tagged with Tree, Depth-First Search, Breadth-First Search. Reported in interviews at Meta and 3 others.
Minimum Depth of Binary Tree shows up at Meta, Uber, Google, and Adobe, and it's marked easy, but half the candidates get it wrong on their first OA attempt. The trap is obvious: you write a standard depth-first traversal and compute the depth of every node, then return the smallest. That works, but it's slow on skewed trees because you touch every single node. The real solution recognizes that minimum depth is the shortest path to a leaf, not the height of the tree, and stops early the moment you find one. If this problem hits your live assessment and you blank on the early-exit pattern, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "Minimum Depth of Binary Tree"
Minimum Depth of Binary Tree 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 for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe key insight is that minimum depth means the shortest path from root to any leaf node, where a leaf has no children. Most candidates conflate it with the minimum height of the entire tree and end up doing unnecessary work. If you use standard DFS without stopping early, you'll traverse all nodes even when a leaf appears at depth 2. The real pattern is a BFS or a DFS that returns as soon as you hit a leaf. On a skewed tree (think a linked-list shape), early exit saves you from visiting all N nodes. Breadth-First Search is especially efficient here because you stop at the first complete level. Candidates who know the distinction between 'minimum depth to any leaf' and 'tree height' rarely stumble. StealthCoder is the hedge for the one candidate who didn't re-read the problem carefully enough on interview day.
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Minimum Depth of Binary Tree recycles across companies for a reason. It's easy-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 for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Depth of Binary Tree interview FAQ
Why is this marked easy if so many people get it wrong on the OA?+
The algorithm is simple (DFS or BFS), but the gotcha is subtle. Most people confuse minimum depth with the minimum height of the entire tree structure, then implement a full traversal. Reading 'minimum depth' as 'shortest path to a leaf' flips the solution from O(N) worst-case to O(h) best-case. The acceptance rate reflects this reading-comprehension trap.
Does BFS really beat DFS for this problem?+
Yes, on typical trees. BFS explores level by level and stops the instant it finds a leaf. DFS can also stop early, but only if you check 'is this a leaf' before recursing deeper. Both are O(h) best-case on balanced trees, but BFS is more intuitive for early exit. The input data shows BFS is listed as a core topic here.
What's the gotcha with a single-child node?+
A node with only a left or right child is not a leaf. A leaf has zero children. If you return depth as soon as you reach a node with one child, you'll get the wrong answer. You must recurse until both left and right are null. This catches candidates who copy-paste minimum-of-two-subtrees logic without re-reading the definition.
Do I need to handle null input?+
Yes. A null tree has no nodes, so minimum depth is 0. A tree with just a root and no children has minimum depth 1. The edge cases are straightforward once you nail the definition of 'leaf' and understand that you're finding the shortest path to one.
Is this still being asked at Google, Meta, and Uber?+
Yes. It appears in reports from all four companies in the input data. It's a screening-round problem, not an advanced one. The acceptance rate hovers just above 50 percent, meaning it's still a real filter for candidates who don't read the problem carefully or who default to textbook tree traversal without thinking about early exit.
Want the actual problem statement? View "Minimum Depth of Binary Tree" on LeetCode →