现服两次店面挂经(求米）

First round:
Given a binary tree, return the values of the outer nodes of the tree clockwise, starting from the root node, in a list. the outer nodes are: 1. nodes visible when you look from left or right of the tree, 2. leaf nodes (nodes with no child node)
I implemented 3 recursive functio

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f parentheses using ITERATIVE method. I can only think of the following method: iterate through number 0-2^(2n), each number bit 1 is ( and bit 0 is ). then filter invalid parentheses. Do you have a better approach? Please share it in comments.

求大米看面经