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11. Same Tree

easyAsked at CircleCI

Check whether two binary trees are structurally and value-wise identical.

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

Constraints

  • 0 <= number of nodes per tree <= 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 as strings and compare.

Time
O(n)
Space
O(n)
function ser(n) { return !n ? '#' : n.val + ',' + ser(n.left) + ',' + ser(n.right); }
return ser(p) === ser(q);

Tradeoff:

2. Recursive structural compare

Compare nodes pairwise; recurse on left and right 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:

CircleCI-specific tips

CircleCI uses tree-equality checks when diffing pipeline config trees — show concrete null-handling rather than vague pseudo-code.

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Output

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