刷题打卡 －pxu

297. Serialize and Deserialize Binary Tree . I thought I've done this but leetcode told me that I didn't. weird though. This should use either preorder or postorder as the inorder seems can not make sure the treenode has the unique structures. for the null node, need to mark as something like '#' so that null could be handled during deseriazation. Good night.

490. The Maze - make sure using visited][] and bound to the end

505. The Maze II, I was using the bfs and it should not use visited[][] to track whether the point has being visisted before as it will have to get the shortest path

42. Trapping Rain Water. Tried both two points and dp solutions and feels good.

4. Median of Two Sorted Arrays  - implemented with binarysearch tree to reach time complexity to log(m+n)

11. Container With Most Water - used two points and make sure compare with height[l] and height[r] , not l and r.

reviewed union-find data structure and algorithm just now. feels good on it.

684. Redundant Connection - resolved by using union find

261. Graph Valid Tree - used union find to resolve it this time. make sure check edge length = n-1

261. Graph Valid Tree -  re-implemented with both BFS and DFS. need to use status to check whether a node has been visited or not