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10. Same Tree

easyAsked at Box

Determine whether two binary trees are structurally identical with the same values — Box uses this when comparing two folder-tree snapshots during a conflict-resolution merge.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given the roots of two binary trees p and q, write a function to check if they are the same or not. Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

Constraints

  • 0 <= number of nodes <= 100
  • -10^4 <= Node.val <= 10^4

Examples

Example 1

Input
p = [1,2,3], q = [1,2,3]
Output
true

Example 2

Input
p = [1,2], q = [1,null,2]
Output
false

Approaches

1. Serialize and compare

Serialize both trees and string-compare.

Time
O(n)
Space
O(n)
function ser(t) { return !t ? '#' : `${t.val},${ser(t.left)},${ser(t.right)}`; }
return ser(p) === ser(q);

Tradeoff:

2. Parallel DFS

Recurse on both trees simultaneously; short-circuit on mismatch.

Time
O(n)
Space
O(h)
function isSameTree(p, q) {
  if (!p && !q) return true;
  if (!p || !q) return false;
  if (p.val !== q.val) return false;
  return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
}

Tradeoff:

Box-specific tips

Box wants the short-circuit recursion verbalized — they map this to early-aborting folder-tree diffs once a single child mismatch is found.

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Output

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