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101. Symmetric Tree 👍

  • Time: $O(n)$
  • Space: $O(h)$
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class Solution {
 public:
  bool isSymmetric(TreeNode* root) {
    return isSymmetric(root, root);
  }

 private:
  bool isSymmetric(TreeNode* p, TreeNode* q) {
    if (!p || !q)
      return p == q;

    return p->val == q->val &&                //
           isSymmetric(p->left, q->right) &&  //
           isSymmetric(p->right, q->left);
  }
};

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class Solution {
  public boolean isSymmetric(TreeNode root) {
    return isSymmetric(root, root);
  }

  private boolean isSymmetric(TreeNode p, TreeNode q) {
    if (p == null || q == null)
      return p == q;

    return p.val == q.val && isSymmetric(p.left, q.right) && isSymmetric(p.right, q.left);
  }
}

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class Solution:
  def isSymmetric(self, root: TreeNode | None) -> bool:
    def isSymmetric(p: TreeNode | None, q: TreeNode | None) -> bool:
      if not p or not q:
        return p == q
      return (p.val == q.val and
              isSymmetric(p.left, q.right) and
              isSymmetric(p.right, q.left))

    return isSymmetric(root, root)

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