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10. Same Tree

easyAsked at GoDaddy

Check if two binary trees are structurally identical with equal node values.

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 when 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

Stringify both trees with null markers and compare strings.

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. Recursive structural compare

Match nulls, then values, then recurse both subtrees.

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:

GoDaddy-specific tips

GoDaddy uses this to model verifying that a master and replica nameserver's hierarchical zone data match exactly before promoting the replica.

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Output

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