每个程序员都应该知道的14个数字（关于算法运行时间的）

14 numbers every developer should know列举了14个数字，可以作为大家设计算法时的一个参考。下表列出了秒数量级下各种算法复杂度能接受的输入个数。

maximum n	complexity	algorithms	data structures
1,000,000,000 and higher	log n, sqrt n	binary search, ternary search, fast exponentiation, euclid algorithm
10,000,000	n, n log log n, n log* n	set intersection, Eratosthenes sieve, radix sort, KMP, topological sort, Euler tour, strongly connected components, 2sat	disjoint sets, tries, hash_map, rolling hash deque
1,000,000	n log n	sorting, divide and conquer, sweep line, Kruskal, Dijkstra	segment trees, range trees, heaps, treaps, binary indexed trees, suffix arrays
100,000	n log2 n	divide and conquer	2d range trees
50,000	n1.585, n sqrt n	Karatsuba, square root trick	two level tree
1000 - 10,000	n2	largest empty rectangle, Dijkstra, Prim (on dense graphs)
300-500	n3	all pairs shortest paths, largest sum submatrix, naive matrix multiplication, matrix chain multiplication, gaussian elimination, network flow
30-50	n4, n5, n6
25 - 40	3n/2, 2n/2	meet in the middle	hash tables (for set intersection)
15 - 24	2n	subset enumeration, brute force, dynamic programming with exponential states
15 - 20	n2 2n	dynamic programming with exponential states	bitsets, hash_map
13-17	3n	dynamic programming with exponential states	hash_map (to store the states)
11	n!	brute force, backtracking, next_permutation
8	nn	brute force, cartesian product