纽约在职刷题

417. Pacific Atlantic Water Flow. DFS. 沿着海边逆流而上，能visit的就是能入海的。

179. Largest Number. Python class inheritance, sorted built in function with key argument and __lt__ class method.

242. Valid Anagram. Dict

592. Fraction Addition and Subtraction. Regular Expression真是道坎。math.gcd(x,y) and //=

311. Sparse Matrix Multiplication. Condition on nonzero elements of one matrix.

457. Circular Array Loop. 感觉还是各种loop，写的不够熟练，各种边界条件，小技巧很容易one off error.

692. Top K Frequent Words. 用Counter, heapq自己写个key，感觉有点虚。

74. Search 2D Matrix. Binary Search平时太懒就用bisect.bisect，还是得自己不时写写。

441. Arranging Coins. Math

16. 3Sum Closest. Two pointers in sorted array.