337. House Robber III

• basic: for each node, you can choose rob or not, based on the parent’s status. return max amount of each choice.
• dp: keep previous rob information.

95. Unique Binary Search Trees II

• foreach 1 to n, generate left and right subtree and combine with current node.

111. Minimum Depth of Binary Tree

• its root to leaf, not to other node. For example (1, 2), the only path is 1->2.