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10. Same Tree

easyAsked at Lyft

Check whether two binary trees are structurally identical with the same 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 if they are structurally identical and the nodes have the same value.

Constraints

  • Number of nodes in both trees in range [0, 100]
  • -10^4 <= node value <= 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 and compare strings.

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 current node values, then recurse left and right in lockstep.

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:

Lyft-specific tips

Lyft asks about tree equality during the diff stage of region-shape comparisons; explicit nullability handling earns bonus signal in the matching service context.

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Output

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