Cool Python Functions

Mar 16, 2023

Python is my main language when I’m solving leetcode problems, because I don’t want to focus too much on language when I’m just trying to nail the quiz. I’ve been leetcoding for a few weeks now and I wanted to show some useful methods that I’ve learned during the process.

I’m writing this more as a personal note than an actual article, with the aim of keeping it up-to-date for my future self. Despite my best efforts, I tend to forget many of these things when I visit Leetcode and I haven’t been practicing in a while.

Some of them are trivial, I know, but I used different ways to get the same result. These are just more elegant and sometimes effortless alternatives.

Last edited 16 Mar 2023

Bit count

(Python >3.10)

n = 4329      # 0b1000011101001
n.bit_count() # 6

Check if str is a number

"10".isnumeric()         # True
"notAnumber".isnumeric() # False

Set Operations

  • Intersection

set([0,1,2]) & set([3,1,2])  # set([1,2])
set([0,1,2]).intersection(set([3,1,2]))

  • Contains

set([1,2,3]) <= set([1,2,3,5,6,7]) # True
set([1]) <= set([2,3])             # False
set([1,2]) < set([1,2])            # False

  • Union

set([1,2]) | set([1,3,4])      # set([1,2,3,4])
set([1,2]).union(set([1,3,4]))

Iterate backwards

There are multiple ways to do this, but this is very nice imo.

arr = [1,2,3,4]
for i in range(len(arr)):
    print(arr[~i]) # 4 3 2 1

Iterate Matrix (single index)

mat = [[0, 2], [3, 4], [5, 0]]
m, n = len(mat), len(mat[0])

for i in range(m * n):
    print(mat[i//n][i%n]) # 0 2 3 4 5 0

Merge two dictionaries

(Python >3.9)

s = {k: 0 for k in "abcd"}
d = {k: 1 for k in "lol"}
z = s | d # {'a':0, 'b':0, 'c':0, 'd':0, 'l':1, 'o':1}

Counter intersections

Final result is going to have the keys that both Counter have, if they have different values the min one is going to be kept.

from collections import Counter

a = Counter(list("heeeere"))  # {h: 1, e: 4, r: 1}
b = Counter(list("here!"))    # {h: 1, e: 2, r: 1, !: 1}
z = a & b                     # {h: 1, e: 2, r: 1}

Permutations & Combinations

import itertools

# Order matters
c = itertools.combinations([0,1,2], 2) # [(0, 1), (0, 2), (1, 2)]

# Order doesn't matter
p = itertools.permutations([0,1,2], 2) # [(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]

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