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11. Same Tree

easyAsked at Brex

Determine whether two binary trees are structurally identical with the same 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 tree. Two binary trees are considered the same if they are structurally identical and the nodes have the same values.

Constraints

  • Nodes in each tree in [0, 100]
  • -10^4 <= node value <= 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

Preorder-serialize each tree to a string and string-compare.

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. Parallel recursion

Recurse both trees together and short-circuit on first 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:

Brex-specific tips

Brex uses this pattern to compare two snapshots of an approval graph before and after a policy change, so call out that you'd hash and cache subtrees to detect drift across thousands of org charts.

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Output

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