【LeetCode OJ】Sum Root to Leaf Numbers

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# Definition for a  binary tree node

# class TreeNode:

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class
Solution:

    # @param root, a tree node

    # @return an integer

    def
sumNumbers(self, root):

        """

        BFS the tree from the root

        track each path as a root->leaf number

        """

        # specail cases

        if
root is
None:

            return
0

        # queue of the numbers

        # BSF the tree

        q =
[ (root, 0) ]

        res =
0

        while
q:

            new_q =
[]

            # expand all paths in q by one step

            for
(node, number) in
q:

                node_number =
number *
10 +
node.val

                # If the node is a leaf, remove this path and record the root-leaf number

                if
node.left ==
node.right ==
None:

                    res +=
node_number

                # Expand the path by left/right children

                else:

                    if
node.left:

                        new_q.append( (node.left, node_number) )

                    if
node.right:

                        new_q.append( (node.right, node_number) )

            # Update the path list

            q =
new_q

        return
res