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Python Tricks for Competitive Programming

Aniruddha Chaudhari/3930/0
CodePython

1. Sort List of Tuples by Second Value in Reverse Order

val = [('v', 3), ('a', 4), ('b', 2)]
val.sort(key = lambda x: x[1], reverse=True)
print(val)

Reference: Sort List of Tuples by First/Second value

2. List of Cubes of First 5 Odd Numbers using List Comprehension

arr = [i*3 for i in range(10) if i%2]
print(arr)

3. Python Dictionary Comprehension

dic = [(i, i*2) for i in range(10)]
print(dict(dic))

4. Python Map Example

print(list(map(lambda x: x*2, range(10))))

Reference: Lambda Function

5. Python Filter Example

print(list(filter(lambda x: x%2, range(10))))

6. Python Reduce Example

from functools import reduce
print(reduce(lambda x,y: x+y, range(10)))

7. Permutation

import itertools
itertools.permutations('ABCD', 2)

Reference: Get permutation of a string

8. Selecting Random Number

import random
print(random.choice(range(1, 10)))

Reference: Selecting random number

9. Get the Frequency of Characters in String

Using Collection Counter

from collections import Counter
print(dict(Counter("ababacd")))
#Counter({'a': 3, 'b': 2, 'c': 1, 'd': 1})

Using List Comprehension

msg = "ababcd"
dic = [(i, msg.count(i)) for i in set(msg)]
print(dict(dic))
#{'c': 1, 'b': 2, 'd': 1, 'a': 2}

10. Convert Python Dict to List

dic = {'a': 3, 'b': 2, 'c': 1, 'd': 1}

# list of dictionary keys
print(list(dic))

# list of dictionary values
print([v for k, v in dic.items()])

11. Convert Integer to Binary String

num = 9
binary_num = bin(num).replace("0b", "")  #1001

These Python Tricks for Competitive Programming will help you for solving competitive coding challenges in coding interviews.

Python Interview Questions eBook

coding challengePython
Aniruddha Chaudhari
I am complete Python Nut, love Linux and vim as an editor. I hold a Master of Computer Science from NIT Trichy. I dabble in C/C++, Java too. I keep sharing my coding knowledge and my own experience on CSEstack.org portal.

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Why?

Why Competitive Programming Important?

Coding Challenges for Practice

  1. Count Common Factor
  2. Does it Divide
  3. Sum of Sub Arrays
  4. Pair of Desired Sum
  5. Remove Duplicate Char from String
  6. Sort String by Char Freq (Python)
  7. Sort String by Char Freq (Java)
  8. Split Array into Equal Sum Subarray
  9. Validate IP Address
  10. Validate PAN Card Number
  11. Validate Sudoku
  12. Sort Circular Rotated Array
  13. String Permutations
  14. Min Arrow to Burst Bubbles
  15. Min Cost to Paint All Houses [Amazon]
  16. HourGlass with Max Sum
  17. Max Profit by Buying/Selling Stocks
  18. Hailstone Sequence
  19. Reverse String without affecting Special Characters
  20. Secure Conversation by Encry/Decry
  21. Special Elements in Matrix
  22. Next Greater No with Same set of Digits
  23. Smallest Subarray with Sum Greater than Given Number
  24. Group Anagrams
  25. Find Duplicates in Array in O(n)
  26. Find Two Unique Numbers from Array in O(n)
  27. Number Patterns & Finding Smallest Number
  28. First Unique Element in a Stream
  29. Flip Equivalent Binary Trees [TeachMint]
  30. Minimum Cost of Merging Files [Amazon]
  31. Minimum Distance for Truck to Deliver Order [Amazon]
  32. Longest Sequence of URLs
  33. Order Task for Given Dependencies
  34. Design Music Player
  35. Multilevel Parking System Design
  36. Minimum Coins Required
  37. Max Sum Subarray
  38. Max Avg Sum of Two Subsequences
  39. Merge Overlapping Intervals
  40. Longest Balanced Substring
  41. Longest Path in a Weighted Tree
  42. Generate Balanced Parentheses
  43. PostOrder Traversal Without Recursion

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