痛定思痛，不忘初心

day 26
sql: window function (row_number(), rank(), dense_rank())
      case when+aggregation
trapping rain water: two pointer, the water per unit is decided by lower height
binary tree path sum
word pattern I: use two hashmaps to store one-to-one matching
square root I: binary search

 许久未登陆，积分回到解放前。虽然没有跟帖打卡，但是依然在坚持刷题，这也许就是坚持一段时间打卡的好处吧。最近有面试，有空写下面筋作为总结。