Python Snippets for Coding Interviews

TOC

Strings

Reverse a String

str = "Hello"
reversed_str = str[::-1]
print(reversed_str)  # Output: "olleH"

Check if a String is a Palindrome

def is_palindrome(s: str) -> bool:
    return s == s[::-1]

s = "racecar"
print(is_palindrome(s))  # Output: True

Sort String

s = "hello"
sorted_s = ''.join(sorted(s))
print(sorted_s)  # Output: "ehllo"

Count Characters in a String

from collections import Counter

s = "hello"
char_count = Counter(s)
print(char_count)  # Output: {'h': 1, 'e': 1, 'l': 2, 'o': 1}

Check is String a Number

a = "10"
print(a.isnumeric()) # True

b = "hi"
print(b.isnumeric()) # False

Conversions

From String to Number

s = "10"
num = int(s)
print(num)  # Output: 10

From Number to String

num = 10
s = str(num)
print(s)  # Output: "10"

Ascii values: ord, chr

# Convert character to ASCII value
char = 'A'
ascii_val = ord(char)
print(ascii_val)  # Output: 65

# Convert ASCII value to character
ascii_val = 65
char = chr(ascii_val)
print(char)  # Output: "A"

Capitalize String

s = "hello"
capitalized_s = s.capitalize()
print(capitalized_s)  # Output: "Hello"

Lists

Reverse a List

arr = [1, 2, 3, 4]
reversed_arr = arr[::-1]
print(reversed_arr)  # Output: [4, 3, 2, 1]

Sort List

arr = [3, 1, 4, 1, 5, 9, 2]
sorted_arr = sorted(arr)
print(sorted_arr)  # Output: [1, 1, 2, 3, 4, 5, 9]

Count Elements in a List

arr = [1, 2, 1, 3, 2, 1, 4]
element_count = Counter(arr)
print(element_count)  # Output: {1: 3, 2: 2, 3: 1, 4: 1}

Iterate over a List

arr = [1, 2, 3, 4]
for num in arr:
    print(num)

List Comprehension

List comprehension is a concise way to create lists in Python. It is similar to using a loop but more compact.

arr = [1, 2, 3, 4]
squared_arr = [num**2 for num in arr]
print(squared_arr)  # Output: [1, 4, 9, 16]

Dictionaries

Iterate over a Dictionary

dict = {'a': 1, 'b': 2, 'c': 3}
for key, value in dict.items():
    print(key, value)

Check if Key Exists in Dictionary

dict = {'a': 1, 'b': 2, 'c': 3}
key = 'a'
if key in dict:
    print(f"{key} exists in the dictionary.")

Get Value for a Key

dict = {'a': 1, 'b': 2, 'c': 3}
key = 'a'
value = dict.get(key)
print(value)  # Output: 1

Sort Dict by Key

dict = {'b': 2, 'a': 1, 'c': 3}
sorted_dict = {k: dict[k] for k in sorted(dict)}
print(sorted_dict)  # Output: {'a': 1, 'b': 2, 'c': 3}

Sort Dict by Value

dict = {'b': 2, 'a': 1, 'c': 3}
sorted_dict = {k: v for k, v in sorted(dict.items(), key=lambda item: item[1])}
print(sorted_dict)  # Output: {'a': 1, 'b': 2, 'c': 3}

Sets

Check if Element Exists in Set

s = {1, 2, 3, 4}
element = 3
if element in s:
    print(f"{element} exists in the set.")

Add Element to Set

s = {1, 2, 3}
s.add(4)
print(s)  # Output: {1, 2, 3, 4}

Matrix

Init 2d Array

rows, cols = 3, 4
matrix = [[0 for _ in range(cols)] for _ in range(rows)]
print(matrix)

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
for row in matrix:
    print(row)

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