Given a binary tree, imagine yourself standing on the left side of it,
return the values of the nodes you can see ordered from bottom to top,
then switch to right side of the tree, and return the values of the nodes you can see ordered from top to bottom.
Binary Tree:
1
/ \
2 3
/ \ / \
6 5 5 4
Answer: [6, 2, 1, 3, 4]
Binary Tree:
1
/ \
2 3
\
5
Answer: [5, 2, 1, 3, 5]
Standing on the left side gives the leftmost node of each level, but the ordering must be reversed from bottom to top. Standing on the right side gives the rightmost node level by level from top to bottom. The problem is solved with BFS level traversal and extracting the appropriate visible node at each level.
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