[FIXED] TypeError: cannot unpack non-iterable TreeNode object

Issue

I am learning to use a deque to check if two binary trees are the same. However, I can't figure out why n1 and n2 (as node1 and node2) can't be unpacked. I tried to put them in a list and a tuple, unpacking, etc, but can't unpack successfully. I'm thinking it's something else. Could anyone help? Here is the code:

    def iterative(self, p, q):
        q = deque( [p, q] )
        while len(q) > 0:
            n1, n2 = q.popleft()
            if not n1 and not n2:    pass
            elif not n1  or not n2:  return False
            else:
                if n1.val != n2.val: return False
                q.append( [n1.left, n2.left] )
                q.append( [n1.right, n2.right] )
        return True

Solution

The problem is in how you initialise the deque. The constructor expects an iterable of entries, and as you intend an entry to be a pair, you need to provide an iterable of pairs. But instead you provided just a pair, which it is interpreted as a sequence of two entries, each being a singe node and not a pair. This means your deque starts out with two entries instead of one, and each entry is a node, not a pair of nodes.

Change this:

q = deque( [p, q] )

to this:

q = deque( [[p, q]] )

Answered By - trincot