Symmetric Tree | Problems

Given the root of a binary tree, determine whether it looks the same when reflected across its vertical center — in other words, whether the left and right subtrees are mirror images of each other.

Input Format

Implement isSymmetric(root). Inputs below show JavaScript function arguments; there is no stdin parsing. Trees use level-order arrays with null for missing children. The editor passes nodes with val, left, and right properties; [] becomes null.

Output Format

Return the result described in the statement.

Sample Input and Output

Example 1 · Run Sample

Input

root = [1,2,2,3,4,4,3]

Output

true

Example 2

Input

root = [1,2,2,null,3,null,3]

Output

false

Constraints

1 <= number of nodes <= 1000
-100 <= Node.val <= 100

Test Cases (2)

Case 1

Args: [[1,2,2,3,4,4,3]] Expected: true

Case 2

Args: [[1,2,2,null,3,null,3]] Expected: false

Topics

Tree Binary Tree DFS

Recursive Mirror Check

javascript

function isSymmetric(root) {
  function isMirror(a, b) {
    if (!a && !b) return true;
    if (!a || !b || a.val !== b.val) return false;
    return isMirror(a.left, b.right) && isMirror(a.right, b.left);
  }
  return isMirror(root, root);
}

Time: O(n) | Space: O(h)

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