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4. Same Tree

easyAsked at Revolut

Check whether two binary trees are structurally and value-identical, a Revolut warm-up that mirrors comparing two ledger snapshots for reconciliation drift.

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 tree. Two trees are the same if they are structurally identical and the nodes have the same values.

Constraints

  • 0 <= node count <= 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 to strings and compare equality.

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 DFS

Walk both trees in lockstep and short-circuit on the first mismatch. Linear time, stack depth equals tree height.

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:

Revolut-specific tips

Revolut frames this as comparing two ledger trees from different regions — explicitly state that minor units must use integer equality, never float, before you write the recursion.

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Output

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