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10. Same Tree

easyAsked at Canva

Decide if two binary trees are structurally and value-equal — Canva uses this to test recursion hygiene around shape comparisons in template trees.

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: identical structure and identical node values at every position.

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 both trees, compare strings.

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. Recursive structural check

If both null, equal. If one null, unequal. Otherwise compare values + recurse both children.

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

Tradeoff:

Canva-specific tips

Canva interviewers like base cases stated explicitly because template-diff systems hinge on rigorous null/empty handling.

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Output

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