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10. Same Tree

easyAsked at Roblox

Check whether two binary trees are structurally identical with matching values.

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

Problem

Given the roots of two binary trees p and q, return true if they are the same — both their structure and node values must match. Empty subtrees must align on both sides.

Constraints

  • 0 <= 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 each tree to a string and compare.

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

Tradeoff:

2. Parallel recursion

Walk both trees in lockstep; bail early on any 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:

Roblox-specific tips

Roblox engineers value the early-bail recursion because it matches how the engine compares prior-tick and current-tick Workspace snapshots for replication.

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Output

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