Count occurrences of a sub-string with one variable character

Given two strings a and b, and an integer k which is the index in b at which the character can be changed to any other character, the task is to check if b is a sub-string in a and print out how many times b occurs in a in total after replacing the b[k] with every possible lowercase character of English alphabet.

Examples:

Input: a = “geeks”, b = “ee”, k = 1
Output: 1
Replace b[1] with ‘k’ and “ek” is a sub-string in “geeks”
“ee” is also a sub-string in “geeks”
Hence the total count is 2

Input: a = “dogdog”, b = “dop”, k = 2
Output: 2
Replace b[2] with ‘g’, “dog” is a sub-string in “dogdog” which appears twice.

Approach: Make a list of all possible versions of the string b by iterating through all the lowercase letters and replacing the k^th i.e. b[k] character in b with the current character.
Then count the number of occurrence of the new string b in the original string a and store it in a variable count. After all the lowercase characters are used, print the count.

Below is the implementation of the above approach:

# Python3 implementation of the approach
import string

# Function to return the count of occurrences
def countOccurrence(a, b, k):

    # Generate all possible substrings to
    # be searched
    x = []
    for i in range(26):
        x.append(b[0:k] + string.ascii_lowercase[i] + b[k + 1:])

    # Now search every substring 'a' and
    # increment count
    count = 0
    for var in x:
        if var in a:
            count += a.count(var)

    return count

# Driver code
a, b = "geeks", "ee"
k = 1
print(countOccurrence(a, b, k))

Output:

2

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