Python Tips and Tricks for Competitive Programming

Python Programming language makes everything easier and straightforward. Effective use of its built-in libraries can save a lot of time and help with faster submissions while doing Competitive Programming. Below are few such useful tricks that every Pythonist should have at their fingertips:

• Converting a number into a List of digits using map() Function: 

Below is the implementation to convert a given number into a list of digits:

Python3

# Python program to convert a
# number to a list of digits

# Given number
n = 123456

# Stores the list of digits
lis = list(map(int, str(n)))

# Print the digits
print(lis)

Output:

[1, 2, 3, 4, 5, 6]

• Converting a sentence into a List of words using split() Function: Below is the implementation to convert a sentence into a list of words:

Python3

# Python program to convert
# a sentence to a list of words

# Given sentence
sentence = "GeeksforGeeks is the computer science portal for geeks"

# Convert the sentence
# into a list of words
lis = list(sentence.split())

# Print the list of words
print(lis)

Output:

['GeeksforGeeks', 'is', 'the', 'computer', 'science', 'portal', 'for', 'geeks']

• Take newline-separated integers as a List: Newline-separated input from the console can be taken in the form of a List using List Comprehension. Below is the implementation to take input of newline-separated integers as a list:

Python3

# Python program to take
# newline-separated input
# in the form of a list

# Given input
n = int(input())

lis = [int(input()) for _ in range(n)]

• Calculating GCD/HCF of two numbers: Gcd of two numbers can be computed in python using a built-in function gcd() offered by the Python Math Module.

Below is the implementation to demonstrate gcd() function: 

Python3

# Python program to demonstrate gcd() function
import math
a = 8
b = 24

# Print the GCD of a and b
print(math.gcd(a, b))

Output:

8

• Print permutations of array: All permutations of an array can be efficiently generated using built-in permutations() method from itertools package. This method takes a List as input and returns an object List of Tuples that contains all permutations.

Below is the implementation of the approach:

Python3

# Python program to print all
# permutations using library function
from itertools import permutations

# Get all permutations of [1, 2, 3]
perm = permutations([1, 2, 3])

# Print the obtained permutations
for i in list(perm):
    print (i)

Output:

(1, 2, 3)
(1, 3, 2)
(2, 1, 3)
(2, 3, 1)
(3, 1, 2)
(3, 2, 1)

• Printing a string multiple times without Loop: Below is the implementation to print a string multiple times without loop using string multiplication technique:

Python3

# Python program to print
# a string given number of times

# Given string
str ="India"

# Print the string 2 times
print(str * 2)

Output:

IndiaIndia

• To print a list with spaces without loop: A list can be printed without running the loop by using the * operator in Python.

Below is the implementation to print a list with spaces without loop: 

Python3

# Python program to print a list with spaces without loop
lis = [1, 2, 3, 4]

# Printing list elements with spaces
print(*lis)

Output:

1 2 3 4

• Convert binary string to decimal: A binary string can be converted to its decimal equivalent using built-in int() function.

Below is the implementation of the above approach: 

Python3

# Python program to convert a
# binary string to its decimal
# equivalent using int() function

# Given string
binary = "1010"

# Print decimal equivalent
print(int(binary, 2))

Output

10

• To print sorted list with spaces: Sorting any sequence is very easy in Python using a built-in method sorted() and using * symbol to print list with spaces. Sorted() sorts any sequence (list, tuple) and always returns a list with the elements in a sorted manner, without modifying the original sequence.

Below is the implementation to print a sorted list with spaces: 

Python3

# Python program to print a sorted list with
# spaces using sorted() function
lis = [6, 2, 7, 3, 4]

# Print the sorted sequence
print(*sorted(lis))

Output:

2 3 4 6 7

• To find common elements in two arrays: The common elements in 2 arrays/lists can be done in a much simpler way using sets. The intersection() function in Python gives the common elements in both arrays/lists.

Below is the implementation to demonstrate intersection() function:

Python3

# Python program to print common elements in
# both the list using intersection() function
array1 = [4, 5, 6, 7, 8]
array2 = [3, 4, 5, 1, 72]

# Print the common elements
print(set(array1).intersection(set(array2)))

Output

{4, 5}