137. binary tree vertical traversal

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Traverse a binary tree vertically from left to right, from top to bottom, the binary tree contains positive integers as node values.

For above binary tree, vertical traversal should return


If two nodes are at the same position, their order should inherit from their parent node. For example, 9 and 10 are at the same position, since 7 is before 8, so 9 should be before 10.

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