Leetcode-Easy 101. Symmetric Tree

class Solution:
    def isSymmetric(self, root):
        if not root:
            return True
        dq = collections.deque([(root.left,root.right),])
        while dq:
            node1, node2 = dq.popleft()
            if not node1 and not node2:
                continue
            if not node1 or not node2:
                return False
            if node1.val != node2.val:
                return False
            # node1的左与node2的右相对陈
            dq.append((node1.left,node2.right))
            dq.append((node1.right,node2.left))
        return True