Symmetric Tree
A easy-tier problem at 59% community acceptance, tagged with Tree, Depth-First Search, Breadth-First Search. Reported in interviews at Comcast and 10 others.
Symmetric Tree is the easy problem that trips up candidates who haven't coded trees in a month. It's asked by Google, Meta, Microsoft, Apple, and LinkedIn regularly, and the acceptance rate sits at 59%, which means nearly half the people who attempt it either time out or submit broken code. The trap is thinking you need to flatten the tree or compare two traversals. You don't. The real pattern is recursive mirror-checking, and if you blank on the structure during your assessment, StealthCoder surfaces a working solution in seconds while the proctor sees only your code editor.
Companies that ask "Symmetric Tree"
Symmetric 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 by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderA symmetric tree is one where the left and right subtrees are mirror images of each other. The trick most candidates miss is that you can't just check if left equals right at each node. Instead, you need a helper function that compares two nodes simultaneously: does the left child of the left subtree match the right child of the right subtree, and vice versa. Both Depth-First Search and Breadth-First Search work, but DFS is cleaner and requires almost no extra space. The common failure mode is trying to serialize or traverse the tree once, then compare results. That's slower and error-prone. If you hit this problem live and the recursive pattern doesn't click immediately, StealthCoder runs invisibly and gives you the helper-function structure so you can type it out and move on.
Pattern tags
You know the problem.
Make sure you actually pass it.
Symmetric 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 by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Symmetric Tree interview FAQ
Is Symmetric Tree still asked at FAANG?+
Yes. Google, Meta, Microsoft, and Apple are all in the input data. It's an easy-tier problem, so it typically shows up as a warm-up or a second problem in a two-problem assessment. Acceptance rate of 59% suggests it's still live and actively filtering candidates.
What's the trick to solving Symmetric Tree in under 5 minutes?+
Use a recursive helper that takes two nodes and checks if they're mirrors. Compare node.left with its counterpart and node.right with its counterpart in a single traversal. No serialization, no extra data structures. Just base cases and recursive calls.
Can you solve this with BFS instead of DFS?+
Yes, but it's messier. BFS requires a queue and you have to pair nodes manually. DFS is faster to code and understand. Both are acceptable, but if you're under time pressure, pick DFS. The input lists both topics as relevant.
How does Symmetric Tree relate to other Binary Tree problems?+
It's a stepping stone to harder tree-comparison problems. If you can code the mirror-check pattern here, you've got the foundation for problems like Maximum Path Sum or Validate BST. It's foundational pattern recognition, not a one-off trick.
What if I freeze on this during the actual assessment?+
That's where the hedge matters. If the recursive structure isn't immediate and you're burning time, StealthCoder reads the problem off your screen and surfaces a working solution invisible to the proctor. You type it in, pass the tests, and move to the next problem.
Want the actual problem statement? View "Symmetric Tree" on LeetCode →