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11. Same Tree

easyAsked at Gojek

Decide whether two binary trees are structurally identical with matching 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 tree. They are the same if they are structurally identical and the nodes have the same value.

Constraints

  • The number of nodes in both trees is in [0, 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 with nulls included and string-compare.

Time
O(n)
Space
O(n)
const s = t => !t ? '#' : `(${t.val},${s(t.left)},${s(t.right)})`;
return s(p) === s(q);

Tradeoff:

2. Parallel recursion

Recurse both trees together; both null is equal, one null is unequal, otherwise check value and recurse children.

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:

Gojek-specific tips

Gojek's multi-service catalog often replicates config trees across regions, so a short-circuiting structural compare is exactly the shape of code that ships.

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Output

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