fails.md

UnionFind.union, without checking rootA != rootB

• P: Number of Connected Components in an Undirected Graph
• when rootA == rootB, union exist already, no need to union again.

Don't forget to map.put(i, new ArrayList<>())

• P: Number of Connected Components in an Undirected Graph
• in DFS approach when initializing the adjacent list: use map.put(x,y), not add

forgot to cast int to char

• P: wordladder
• sb.setCharAt(i, (char) j + 'a');
• Given input list: list.contains(), list.remove() are O(logn)!!!
• Make sure to convert it to HashSet() if need to use contains()/remove()

Check input range for SegmentTree problem

• P: Segment Tree Query II
• Forgot to validate [start, end] range.
• Need to fail if completely out of range, or override one side of the range if partial of the range is applicable

Jump too fast into 1 approach

• P: Max Points on a line
• Jump too fast into DP, when seeing a board, but ignored the fact: it's not nxn and not applicable.

正数/负数

• P: Expression Add Operators
• dfs都对, 但是负数的地方, 忘记加符号: be consistent and mindful about negative number
• dfs(rst, list, s, i + 1, sum - currValue, - currValue, target);

i++, i--, testing

• code快, 写错++, --
• testing时候忽略了++,--, 那么其实就没有在真的test.

Doubly Link BST

• 问清楚, 最后的 head 跟 tail也要link在一起
• 在DFS中, 当dfs的结果出来以后(right or left linked list), 其实就可以利用结果的性质, 而不用再重新干做.
• leftTail = leftHead.left, rightTail = rightHead.left