二叉树 06. 对称二叉树

方法一：递归  时间复杂度O(N)  空间复杂度O(N)

def isSymmetric(root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        def sym(l,r):
            if not l and not r:
                return True
            if l and r and l.val == r.val:
                return sym(l.left,r.right) and sym(l.right,r.left)
            return False
        return sym(root.left,root.right)

 方法二：队列  时间复杂度O(N)  空间复杂度O(N)　　成对进出

def isSymmetric(root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root is None:
            return True

        queue = []
        queue.append(root.left)
        queue.append(root.right)
        while queue != []:
            l = queue.pop(0)
            r = queue.pop(0)
            if l is None and r is None:
                continue
            if (l is None) ^ (r is None):
                return False
            if l and r and l.val != r.val:
                return False
            queue.append(l.left)
            queue.append(r.right)
            queue.append(l.right)
            queue.append(r.left)
        return True