[第二期活动] 在职刷题打卡，目标工作日一天2题，周末一天5题

Day 7

Restore IP Addresses
Letter Combinations of a phone number
binary watch

#Day_3

341. Flatten Nested List Iterator
430. Flatten A Multilevel Doubly LinkedList

Reviewed:
5.Longest Palindromic Substring
973. K Closest Points To Origin

#Day_13

Finished * 2
393. UTF-8 Validation
127. Word Ladder

Day 8

Word Pattern II
Unique Morse Code Words

How to represent Graph in code

Day_2 (8/14)

Valid Number // corner cases like " ", ".", "e", "+","-"
Unique word abbreviation

day 11
UTF-8 Validation
Lowest Common Ancestor of a Binary Search Tree

Day # 3
Valid Parentheses
remove invalid parentheses

#Day_4

1086. High Five
209. Minimum Size Subarray Sum

#Day_14

Finished * 2
126. Word Ladder II
221. Maximal Square

Inorder Successor in BST 复习了iterative的三序遍历树
Lowest Common Ancestor of a Binary Tree 递归和iterative两种方法做了，这个iterative是一边遍历一边做一个child-parent的表，以便于回头遍历，这个方法有点意思