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LeetCode101. 对称二叉树 (递归) + (迭代)

• 递归

class Solution:    def isSymmetric(self, root):        """        :type root: TreeNode        :rtype: bool        """        if root:            return self.dfs(root.left, root.right)        if not root:            return True    def dfs(self, l: TreeNode, r: TreeNode):        if l and r:            return l.val == r.val and self.dfs(l.left, r.right) and self.dfs(l.right, r.left)        else:            return not l and not r

• 迭代

class Solution:    def isSymmetric(self, root):        """        :type root: TreeNode        :rtype: bool        """        if not root:            return True        q = [root.left, root.right]        while q:            t1 = q.pop()            t2 = q.pop()            if not t1 and not t2:                continue            elif t1 == None or t2 == None:                return False            elif t1.val != t2.val:                return False            q.append(t1.left)            q.append(t2.right)            q.append(t1.right)            q.append(t2.left)        return True

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