Symmetric Tree

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center). ### Constraints - The number of nodes in the tree is in the range `[1, 1000]`. - `-100 <= Node.val <= 100` ### Input Format A single line containing space-separated integers representing the tree in level-order (-1 for null). ### Output Format Print `true` if the tree is symmetric, otherwise `false`.