Symmetric Tree

1，題目要求 Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center). 給定二叉樹，檢查它是否是自身的鏡像（即，圍繞其中心對稱）。 For example, this binary tree [1,2,2,3,4,4,3] is symmetric: But the

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