Skip to main content

10. Same Tree

easyAsked at Booking

Decide if two binary trees match — Booking uses this to gauge whether you can compare cached vs live availability 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 structurally identical and the nodes have the same value.

Constraints

  • 0 <= each tree's 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

Preorder-serialize each tree to a string and compare — uses extra memory.

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

Tradeoff:

2. Recursive structural compare

Walk both trees in parallel and short-circuit on 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:

Booking-specific tips

Booking will steer this toward 'how would you diff a cached availability tree against a fresh one' — emphasize the early-exit on mismatch for low-latency search responses.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Same Tree and other Booking interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →