7月缺米的来刷题/Mock interview活动

Day 17, solved 6 problems (solved find duplicate subtree yesterday, so count it out).

Tips:

1. LC 886, need to be familiar with the related graph algorithm first to do it;
2. LC 692, using TreeSet will result a code shorter than using PQ;
3. LC 1047, try to solve it by different ways.

July day6

today mark!

07/09
打卡第8天
Inorder traversal iterative
K Closest Elements in BST
Maximum Width of Binary Tree （recursive/iterative）
关于tree的题目都用iterative和recursive两种方法写一下

7.9 打卡第三天
Mock了Product of Array Except Self，虽然做过了但是真是一点也没想起来。靠面试官一步步引导最后也做出最优解来了。开心，又有了好多自信~

DAY 4 :

Some Notes:
【Medium 】184. Department Highest Salary
            JOIN
                            Department d ON e.DepartmentId = d.Id
            WHERE (Salary, DepartmentId ) IN
                                    (SELECT MAX(Salary), DepartmentId  ..)
        和起来两个table，JOIN ON WHERE
        一部分要求需要‘套娃’，就是需要的几个项，对应起来

【Easy】196. Delete Duplicate Emails
       选某一个table的全部，写作：DELETE p1.*

7月打卡第六天，5题：687， 572， 671，501，690

1. 没有想到有一天我竟然因为 Deque 的发音陷入了沉思。。。😔

2. 第一次遇到把不同结构抽象为树进行处理的问题，思路扩展了哦～

3.  BFS和DFS还是不熟练，接下来多练练。

7/9/20

269. Alien Dictionary
Get edges from neighboring word pairs. Topological sort with min heap
注意[‘abc’, ‘ab’]这种invalid edge，直接返回“”

124. Binary Tree Maximum Path Sum
helper function returns maximum path sum and maximum sum from root to any node
for empty input return -sys.maxsize (题目要求path不为空) and 0
l1, l2 = self.helper(root.left)
r1, r2 = self.helper(root.right)
return max(l1, r1, l2 + root.val + r2), max(l2 + root.val, r2 + root.val, 0)
这题容易写错


146 LRU Cache
Linked list + hash table
Linked list node存key，value
Hash table存mapping from key to previous node

20200708:
3: 0662
4: 0139, 0632, 0698, 1192, 1235
5: 0140

打卡 7.9 Day9
今日终于完成binary search卡，最后四题hard level的practice，难点都在于如何把问题转换为一个monotonic的function。
以及July challenge: Maximum Width of Binary Tree, 用BFS 即可