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Python – Number of positions where Substrings Match of Length K

  • Last Updated : 02 Sep, 2020

Given 2 Strings, count positions where substrings of Length K Match.

Input : test_str1 = ‘geeksforgeeks’, test_str2 = ‘peeksformeeks’, K = 4
Output : 4
Explanation : 4 positions match K length Substings.

Input : test_str1 = ‘geeksforgeeks’, test_str2 = ‘peeksformeeks’, K = 5
Output : 3
Explanation : 3 positions match K length Substings.

Method #1 : Using list comprehension + min() + slicing

In this, we iterate through strings till length of minimum string, and the comparison is done by slicing using string slicing. Iteration is done through loop inside list comprehension.



Python3




# Python3 code to demonstrate working of 
# Number of positions where Substrings Match of Length K
# Using list comprehension + min() + slicing
  
# initializing strings
test_str1 = 'geeksforgeeks'
test_str2 = 'peeksformeeks'
  
# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))
  
# initializing K 
K = 3 
  
# checking for substrings, 
# using len() to get total count
res = len([test_str1[idx : idx + K] for idx in range(min(len(test_str1), len(test_str2)) - K - 1)
        if test_str1[idx : idx + K] == test_str2[idx : idx + K]])
  
# printing result 
print("Number of positions of matching K length Substrings : " + str(res)) 
Output
The original string 1 is : geeksforgeeks
The original string 2 is : peeksformeeks
Number of positions of matching K length Substrings : 5

Method #2 : Using map() + list comprehension

In this, we extract all K length substrings of one string and then using in operator and map, check for each substring if present in other String, this ignores the positional factor of problem.

Python3




# Python3 code to demonstrate working of 
# Number of positions where Substrings Match of Length K
# Using map() + list comprehension
  
# initializing strings
test_str1 = 'geeksforgeeks'
test_str2 = 'peeksformeeks'
  
# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))
  
# initializing K 
K = 3 
  
# Extracting Substrings
subs_str = [test_str1[idx : idx + K] for idx in range(len(test_str1) - K - 1)]
  
# checking in other string
# using count() to get number
res = list(map(lambda ele: ele in test_str2, subs_str)).count(True)
  
# printing result 
print("Number of positions of matching K length Substrings : " + str(res)) 
Output
The original string 1 is : geeksforgeeks
The original string 2 is : peeksformeeks
Number of positions of matching K length Substrings : 5

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