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11. Same Tree

easyAsked at Wix

Determine if two binary trees are identical; Wix uses the same shape check when diffing draft vs published template 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 node values match.

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 + compare

Serialize each tree to a string and compare.

Time
O(n)
Space
O(n)
function ser(n){return n? `(${n.val},${ser(n.left)},${ser(n.right)})` : 'N'}; return ser(p)===ser(q);

Tradeoff:

2. Recursive structural

Recurse on children only when both exist with same val.

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

Tradeoff:

Wix-specific tips

Wix favors the structural recursion answer — they like seeing you handle the null/null base case explicitly because it mirrors their null-component slots.

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Output

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