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10. Same Tree

easyAsked at Chegg

Check whether two binary trees are structurally identical with equal values — Chegg uses this to verify recursion fluency on duplicate-content checks.

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 value.

Constraints

  • 0 <= nodes <= 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

DFS serialize each tree to 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. Recursive structural compare

Both null = true; one null = false; values must match and children must recursively match.

Time
O(n)
Space
O(h)
function isSameTree(p, q) {
  if (!p && !q) return true;
  if (!p || !q) return false;
  return p.val === q.val
    && isSameTree(p.left, q.left)
    && isSameTree(p.right, q.right);
}

Tradeoff:

Chegg-specific tips

Chegg likes the direct structural recursion because their duplicate-content detector compares parsed equation trees node-by-node without ever materializing a serialized form.

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Output

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