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10. Same Tree

easyAsked at TripAdvisor

Check whether two binary trees are structurally identical and have equal node values.

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. Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

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 (preorder with null markers) and compare strings.

Time
O(n)
Space
O(n)
const ser = (n) => n ? `${n.val},${ser(n.left)},${ser(n.right)}` : '#';
return ser(p) === ser(q);

Tradeoff:

2. Recursive structural check

Both null = equal. One null = false. Else value + left + right.

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

Tradeoff:

TripAdvisor-specific tips

TripAdvisor uses tree-equality checks to test if you can verify itinerary structure parity across replicated geo-shards.

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Output

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