缺大米的请参加这个刷题/Mock interview活动

打卡两天的内容：medium和hard果然不适合我，哭哭。。。。
我比较喜欢在select里定义feature，但是实际上可以在from里直接重新定义数据集，看起来思路也更清晰，只是写code的时候需要从后往前写。

打卡 day 14

6.15 3题 第15天

6/15/20

82. Single Number
One pass, constant extra space
Make use of the ^ (xor) operator

560. Subarray Sum Equals K
Hash map from presum to index list. The rest is similar to 2sum.

253. Meeting Rooms II
Line sweep.
Record start and end of interval as two events (class event: time, flag = 1 for event start, -1 for event end)
Sort events by time. Get max number of room needed.

Day 1 (06/15)

刷题6道

takeaways
Remove Duplicates from Sorted Array: two pointers
Best Time to Buy and Sell Stock II
Rotate Array: reverse
Contains Duplicate: hashmap
Single Number：xor
Intersection of Two Arrays II: hashmap or two-pointers


谢谢楼主

打卡第九天
658， 278， 1300

6-14 打卡

6-15 打卡

0615 打卡6道search，基本都是用回溯做

断更之后重新来！
Day 1:

23. Merge k Sorted Lists
可以用dict 或者sorted list

134. Gas station

116. Populating Next Right Pointers in Each Node
翻转链表的三种方法： 用栈作为翻转的辅助； 尾插法，始终把头部节点挪到尾部节点的后面； 递归法