[swift] LeetCode 101. Symmetric Tree

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree is symmetric:

1
/ \
2 2
/ \ / \
3 4 4 3
But the following is not:
1
/ \
2 2
\ \
3 3
Note:
Bonus points if you could solve it both recursively and iteratively.

func isSymmetricTree(_ p: TreeNode?, _ q: TreeNode?) -> Bool {
    if let p = p, let q = q {
        return p.val == q.val && isSymmetricTree(p.left, q.right) && isSymmetricTree(p.right, q.left)
    } else {
        return p == nil && q == nil
    }
}

func isSymmetric(_ root: TreeNode?) -> Bool {
    return isSymmetricTree(root?.left, root?.right)
}

func isSymmetricTree(_ p: TreeNode?, _ q: TreeNode?) -> Bool {

if let p = p, let q = q {

return p.val == q.val && isSymmetricTree(p.left, q.right) && isSymmetricTree(p.right, q.left)

} else {

return p == nil && q == nil

}

func isSymmetric(_ root: TreeNode?) -> Bool {

return isSymmetricTree(root?.left, root?.right)

}

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