- binary index tree, segment tree: LC-315
- topological sorting
- Trie
- Union Find
- KMP
- BFS, DFS
- from collections import Counter, defaultdict, OrderedDict, namedtuple, deque;
- from bisect import bisect_left, bisect_right, insort_left, insort_right
- from heapq import heapify, heappush, heappop, heapreplace