Coding Questions X - 2024

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Get the top 3 most frequent characters of a string

import collections
name = "aabbbccde"

def get_top(d, n):
    print(f"input dictionary d = {d}")
    # sorted list of tuples
    st = sorted(d.items(), key=lambda x:x[1], reverse=True)
    print(f"sorted tuples = {st}")
    return st[0:n]

# method 1
dict_1 = dict(collections.Counter(name))
top3_1 = get_top(dict_1, 3)
print(f"top3_1 = {top3_1}")


# method 2
dict_2 = collections.defaultdict(int)
for c in name:
    dict_2[c] += 1
top3_2 = get_top(dict(dict_2), 3)
print(f"top3_2 = {top3_2}")

# method 3
dict_3 = dict.fromkeys(name,0)
for c in name:
    dict_3[c] += 1
top3_3 = get_top(dict_3, 3)
print(f"top3_3 = {top3_3}")

Output:

input dictionary d = {'a': 2, 'b': 3, 'c': 2, 'd': 1, 'e': 1}
sorted tuples = [('b', 3), ('a', 2), ('c', 2), ('d', 1), ('e', 1)]
top3_1 = [('b', 3), ('a', 2), ('c', 2)]
input dictionary d = {'a': 2, 'b': 3, 'c': 2, 'd': 1, 'e': 1}
sorted tuples = [('b', 3), ('a', 2), ('c', 2), ('d', 1), ('e', 1)]
top3_2 = [('b', 3), ('a', 2), ('c', 2)]
input dictionary d = {'a': 2, 'b': 3, 'c': 2, 'd': 1, 'e': 1}
sorted tuples = [('b', 3), ('a', 2), ('c', 2), ('d', 1), ('e', 1)]
top3_3 = [('b', 3), ('a', 2), ('c', 2)]

Just seen and ever seen

ss = 'AAAABBBCCDAABBBCCC'

# → A B C D A B C
justseen = [ss[0]]
for s in ss:
    if s != justseen[-1]:
        justseen.append(s)
print(f"justseen = {justseen}")

# → A B C D 
everseen = []
for s in ss:
    if s not in everseen:
        everseen.append(s)
print(f"everseen = {everseen}")

Output:

justseen = ['A', 'B', 'C', 'D', 'A', 'B', 'C']
everseen = ['A', 'B', 'C', 'D']

Capitalizing the full name

string.capitalize() capitalizes the first character while string.upper() capitalizes all characters of a string!

fullname = 'albert einstein'
print(f"fullname = {fullname}")
fist_last = fullname.split()

for i in range(len(fist_last)):
    fist_last[i] = fist_last[i].capitalize()
    
fullname_capitalized = ' '.join(fist_last)
print(f"fullname_capitalized = {fullname_capitalized}")

Output:

fullname = albert einstein
fullname_capitalized = Albert Einstein

Counting Consequitive Characters

'abbbcaa' -> (1,'a') (3,'b') (1,'c') (2,'a'): 'a' appears once, 'b' three times, 'c' once, and then 'a' 2 times.

# 'abbbcaa' -> (1,'a') (3,'b') (1,'c') (2,'a')

s = 'abbbcaa'

c = s[0]
count = 1
output = []
for i in range(1,len(s)):
    if c != s[i] or i == len(s)-1:  # new char or end_of_string
        output.append(str((count,c)))
        count = 1
        c = s[i]
    else:
        count += 1
print(f"output = {output}")
final_output = ' '.join(output)
print(f"final_output = {final_output}")

Output:

output = ["(1, 'a')", "(3, 'b')", "(1, 'c')", "(1, 'a')"]
final_output = (1, 'a') (3, 'b') (1, 'c') (1, 'a')

Calculate Product of a List of Integers Provided using input()

# A = [1, 2], B = [3, 4] 
# input:
#       1 2
#       3 4
# Output:
#       AxB = [(1, 3), (1, 4), (2, 3), (2, 4)]

# reading input string of numbers and convert it into a list of integers
number_str_a = input('Enter two numbers separated by a space: ').split()
number_str_b = input('Enter two numbers separated by a space: ').split()
A = [int(x) for x in number_str_a]
B = [int(x) for x in number_str_b]
print(f"A = {A}, B = {B}")

# construct a product using list comprehension
AB = [(x,y) for x in A for y in B]
print(f"AxB = {AB}")

Output:

A = [1, 2], B = [3, 4]
AxB = [(1, 3), (1, 4), (2, 3), (2, 4)]

How many times a substring appears in a string

For example, for a given string, 'ABCDCDC', we want to find the number of times that a substring, 'CDC' occurs in the string. In this case, 'ABCDCDC' and ABCDCDC', so the answer is 2.

Now, find the same substring 'CDC' in a string of 'ABCDCDCCACDCB'

s = 'ABCDCDCCACDCB'
sub = 'CDC'

count = 0
for i in range(len(s)-2):
    if s[i:i+len(sub)] == sub:
        count += 1

print(f"count = {count}")

Output:

count = 3

String validators

Use the following str.isalnum(), str.isalpha(), str.isdigit(), str.islower(), and str.isupper() string validators, read an input string, and then print out True/False per line. Note that the validators return True if all characters of a string satisfy the condition.

True if string has any alphanumeric characters. Otherwise, False.
True if string has any alphabetical characters. Otherwise, False.
True if string has any digits. Otherwise, False.
True if string has any lowercase characters. Otherwise, False.
True if string has any uppercase characters. Otherwise, False.

Note the word any!

def str_validation(s):
    if any([c.isalnum() for c in s]):
        print(f"True")
    else:
        print(f"False")
    if any([c.isalpha() for c in s]):
        print(f"True")
    else:
        print(f"False")
    if any([c.isdigit() for c in s]):
        print(f"True")
    else:
        print(f"False")
    if any([c.islower() for c in s]):
        print(f"True")
    else:
        print(f"False")
    if any([c.isupper() for c in s]):
        print(f"True")
    else:
        print(f"False")

if __name__ == '__main__':
    s = input("Enter a string (alphanumeric, etc...): ")
    str_validation(s)

Output #1:

Enter a string (alphanumeric, etc...): A1a
True
True
True
True
True

Output #2:

Enter a string (alphanumeric, etc...): 123
True
False
True
False
False

Output #3:

Enter a string (alphanumeric, etc...): Abc
True
True
False
True
True

Finding indices that a char occurs in a list

We have two lists: A = ['a', 'a', 'b', 'a', 'b', 'a', 'b'] and B = ['a', 'b', 'c']. Find the positions where each character in B appears in A. For example, the character 'a' from B appears in A at index positions 0, 1, 3, and 5. If a character in B, like 'c', is not found in A, the index should be -1.

from collections import defaultdict    

A = ['a', 'a', 'b', 'a', 'b', 'a', 'b']
B = ['a', 'b', 'c']

d = defaultdict(list)
for y in B:    
    d[y] = [i for i,v in enumerate(A) if v == y]
    if y not in A:
        d[y] = -1

for i in d.items():
    print(i)

Output:

('a', [0, 1, 3, 5])
('b', [2, 4, 6])
('c', -1)

itertools combinations

Print all possible combinations of the input string characters, up to size n.

from itertools import combinations

inp = input('Enter a string and an integer k: ').split()
print(f"inp = {inp}")
s = inp[0]; n = int(inp[1])
print(f"s = {s}, n = {n}")

# Print all possible combinations of chars of the input string, 
# up to size n.

a = []
for i in range(n):
    a.extend(list(combinations(s,i+1)))  
print(f"a = {a}")

aa = []
for x in a:
    aa.append(''.join(x))
print(f"aa = {aa}")

Output:

Enter a string and an integer k: abc 2
inp = ['abc', '2']
s = abc, n = 2
a = [('a',), ('b',), ('c',), ('a', 'b'), ('a', 'c'), ('b', 'c')]
aa = ['a', 'b', 'c', 'ab', 'ac', 'bc']