General Conclusion

O( 1)

O( log n): binary search, heap operations,

O(n): array, hashmap, one pass, two pointer, bucket sort,

O( n log n): merge sort, quick sort, heap sort, array + binary search

O( $$n^2$$ ): 3 pointers, dynamic programming

O( 2 ^ n) : subsets and permutations

BFS, DFS 看情况