Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
For example: Given the below binary tree and sum = 22,
5
/ \
4 8
/ / \
11 13 4
/ \ / \
7 2 5 1
return
[
[5,4,11,2],
[5,8,4,5]
]
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