![Time Complexity
CPython -> list
Append[1] -> O(1)
Get Item -> O(1)
Sort -> O(n log n)
https://wiki.python.org/moin/TimeComplexity](https://image.slidesharecdn.com/diayymbtmg0t85qytwql-signature-bf6db970788daea59a47691761b4a489f2cf5745506c317f3d3dfcd77831fa84-poli-181004132628/85/Andrii-Soldatenko-Competitive-programming-using-Python-29-320.jpg)
Andrii Soldatenko "Competitive programming using Python"
- 1. Competitive Programming using Python Andrii Soldatenko 29 September 2018 OdessaPY ‘18 @a_soldatenko
- 2. Andrii Soldatenko • Contributor in OpenAPI, Golang, Pyhelm, python-sendgrid, tutorial of aiohttp, ansible, requests, etc. • Speaker at many PyCons, committee member of PyCon Belarus and PyCon Russia and open source contributor • blogger at https://asoldatenko.com @a_soldatenko
- 8. @a_soldatenko Anatomy of a Programming Contest Problem • Background story / Summary • Input and Output description • Sample Input/Output • Hints/Pictures
- 9. @a_soldatenko How it looks like?
- 11. top500 ~500 problem solved
- 12. 0 5000 10000 15000 20000 25000 30000 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 Number of contestants used Python compare to other languages C C++ Java Python
- 13. Tip 1: Type code faster https://www.typingtest.com/
- 16. Tip 2: Do Algorithm analysis
- 17. Time complexity O( . . . )
- 18. for i in range(n): pass
- 19. for i in range(n): pass O(n)
- 20. for i in range(n//2): pass
- 21. for i in range(n//2): pass O(n)
- 22. for i in range(n+2): pass
- 23. for i in range(n+2): pass O(n)
- 24. for i in range(n): for j in range(n):
- 25. for i in range(n): for j in range(n): O(n2 )
- 26. def foo(n): if n == 1: return foo(n-1) foo(n-1)
- 27. function call number of calls foo(n) 1 foo(n-1) 2 …. … foo(1)
- 28. function call number of calls foo(n) 1 foo(n-1) 2 …. … foo(1) 2n − 1
- 29. Time Complexity CPython -> list Append[1] -> O(1) Get Item -> O(1) Sort -> O(n log n) https://wiki.python.org/moin/TimeComplexity
- 31. Problem types: • Ad hoc • Complete Search (Iterative/Recursive) • Divide and Conquer • Dynamic Programming
- 32. Problem types: • String Processing • Computational Geometry • Graph • Mathematics
- 33. @a_soldatenko Tip 5: Master Your Programming Languages
- 34. @a_soldatenko
- 36. Tip 6:
- 37. @a_soldatenko Input / Output Routines: Sample input: 3 1 2 5 7 6 3
- 38. @a_soldatenko Input / Output Routines: input() sys.stdin open(‘sample.in’)
- 39. @a_soldatenko Please don’t use prints for debugging
- 40. $ python main.py < sample.in > /Users/andrii/fan/fan/uva_answers/000/ main.py(6)main() 5 import ipdb; ipdb.set_trace() ----> 6 for line in sys.stdin: 7 print(line) ipdb> *** SyntaxError: invalid syntax ipdb> *** SyntaxError: invalid syntax
- 41. @a_soldatenko Simple tip: def fopen(filename, default=sys.stdin): try: f = open(filename) except FileNotFoundError: f = default return f
- 42. @a_soldatenko Simple tip: $ python main.py > /Users/andrii/fan/fan/uva_answers/000/ main.py(13)main() 12 import ipdb; ipdb.set_trace() ---> 13 for line in fopen('sample.in'): 14 print(line)
- 44. 195 - Anagram Given the word “abc”, your program should — by exploring all different combination of the three letters — output the words “abc”, “acb”, “bac”, “bca”, “cab” and “cba”. https://uva.onlinejudge.org/external/1/195.pdf
- 45. int main() { string s = "aba"; sort(s.begin(), s.end()); do { cout << s << 'n'; } while(next_permutation(s.begin(), s.end())); } // aab // aba // baa @a_soldatenko
- 46. from itertools import permutations def main(): for perm in permutations('aba'): print(''.join(perm))
- 47. # aab # aab # aba # aba # baa # baa from itertools import permutations def main(): for perm in permutations('aba'): print(''.join(perm))
- 49. Serhiy Storchaka proposed in python-ideas to add: • factorial(n) • gcd(n, m) • as_integer_ration(x) • binom(n, k) • isprime(n) • primes()
- 50. @a_soldatenko