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Symmetric Tree
Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).
Return true if the tree is symmetric, false otherwise.
Input convention. The tree is passed as a level-order array with null for missing children.
Examples
Constraints
- The number of nodes in the tree is in the range [1, 1000].
- -100 <= Node.val <= 100
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Your approach
- Pattern:Depth-First Search
- Time:O(N)
- Space:O(1)
Complete approach — pattern and complexity both named.
Coach
What you got right
You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.
Where it diverged
No divergence detected. The code correctly aligns with the stated approach.
Next attempt: focus on
Try solving related sliding window problems to build familiarity with two-pointer variants.
Signals
No signals fired — clean run, you stayed in flow.