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10. Same Tree

easyAsked at Zoom

Check whether two binary trees are structurally and value-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. Two trees are the same if they are structurally identical and the corresponding 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

JSON-stringify both trees and compare strings.

Time
O(n)
Space
O(n)
return JSON.stringify(p)===JSON.stringify(q);

Tradeoff:

2. Parallel recursion

Recurse both trees together, short-circuiting on any mismatch.

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:

Zoom-specific tips

Zoom uses tree-equality checks to compare client-side vs server-side room hierarchies after reconnection — explain how early termination saves bandwidth during diff sync.

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Output

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