Python – Remove similar index elements in Strings

Given two strings, removed all elements from both, which are the same at similar index.

Input : test_str1 = ‘geels’, test_str2 = ‘beaks’ 
Output : gel, bak 
Explanation : e and s are removed as occur in same indices. 

Input : test_str1 = ‘geeks’, test_str2 = ‘geeks’ 
Output : ”, ” 
Explanation : Same strings, all same index, hence removed.

Method #1 : Using loop + zip() + join()

In this, we pair elements with its index using join(), and check for inequality to filter only dissimilar elements in both strings, join() is used to convert result in strings.

Python3

# Python3 code to demonstrate working of
# Remove similar index elements in Strings
# Using join() + zip() + loop

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

# conversion to list for zipping
list1 = list(test_str1)
list2 = list(test_str2)
res1 = []
res2 = []
for ch1, ch2 in zip(list1, list2):

    # check inequalities
    if ch1 != ch2:
        res1.append(ch1)
        res2.append(ch2)

# conversion to string
res1 = "".join(res1)
res2 = "".join(res2)

# printing result
print("Modified String 1 : " + str(res1))
print("Modified String 2 : " + str(res2))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

Method #2: Using list comprehension

Performs task using similar method as above, just one-liner to perform task in compact form.

Python3

# Python3 code to demonstrate working of
# Remove similar index elements in Strings
# Using list comprehension

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

# one-liner to solve problem
res = ["".join(mastr) for mastr
      in zip(*[(a, b) for a, b in zip(test_str1, test_str2) if a != b])]

# printing result
print("Modified String 1 : " + str(res[0]))
print("Modified String 2 : " + str(res[1]))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

Time Complexity: O(n)
Auxiliary Space: O(n)

Method #3:  Using index() and replace() methods

Python3

# Python3 code to demonstrate working of
# Remove similar index elements in Strings

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

# conversion to list for zipping
for i in test_str1:
    if i in test_str2:
        if(test_str1.index(i)==test_str2.index(i)):
            test_str1=test_str1.replace(i,"",1)
            test_str2=test_str2.replace(i,"",1)


# printing result
print("Modified String 1 : " + str(test_str1))
print("Modified String 2 : " + str(test_str2))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

Method #4: Using enumerate() function

Step-by-step approach:

1. Initialize the two given strings.
2. Iterate through the characters of the strings using enumerate() and list comprehension.
3. For each character, compare it with the character at the corresponding index in the other string.
4. If they are not equal, add the character to a list.
5. Join the characters in the list to form the modified strings.
6. Print the modified strings.

Below is the implementation of the above approach:

Python3

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

res1 = ''.join(])
res2 = ''.join(])

# printing result
print("Modified String 1 : " + str(res1))
print("Modified String 2 : " + str(res2))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

Time Complexity: O(n), where n is the length of the strings.
Auxiliary Space: O(n), where n is the length of the strings.

Method #5: Using map() + lambda function + zip() + join()

Step-by-step approach:

• Initialize two strings test_str1 and test_str2 
• Create two lists list1 and list2 by using the map() function to apply a lambda function
• Zip the two lists list1 and list2 together using zip() to get a list of tuples
• Use another map() function to apply a lambda function to each tuple in the zipped list
• Join the resulting list of characters from the previous step using the join() function to get the modified strings.
• Print the modified strings.

Below is the implementation of the above approach:

Python3

# Python code to demonstrate working of
# Remove similar index elements in Strings
# Using map() + lambda function + zip() + join()

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

# conversion to list and mapping and joining
res1 = ''.join(list(map(lambda i, j: i if i != j else '', test_str1, test_str2)))
res2 = ''.join(list(map(lambda i, j: i if i != j else '', test_str2, test_str1)))

# printing result
print("Modified String 1 : " + str(res1))
print("Modified String 2 : " + str(res2))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

The time complexity of this approach is O(n), where n is the length of the input strings.
The auxiliary space is also O(n), since we create a new string of length n to store the result.

Method 6:  use the built-in filter() function. 

Step-by-step approach:

• Initialize an empty string to store the result.
• Use the filter() function to create a filter object that only keeps characters that are not similar in index in both strings.
• Use the join() function to convert the filtered object into a string.

Below is the implementation of the above approach:

Python3

# initializing strings
test_str1 = 'geeks'
test_str2 = 'beaks'

# printing original strings
print("The original string 1 is : " + str(test_str1))
print("The original string 2 is : " + str(test_str2))

# creating a filter object to remove similar index elements
filter_obj1 = filter(lambda x: x[0] != x[1], zip(test_str1, test_str2))
filter_obj2 = filter(lambda x: x[0] != x[1], zip(test_str2, test_str1))

# converting the filter object to a string
res1 = ''.join([x[0] for x in filter_obj1])
res2 = ''.join([x[0] for x in filter_obj2])

# printing the modified strings
print("Modified String 1 : " + str(res1))
print("Modified String 2 : " + str(res2))

Output

The original string 1 is : geeks
The original string 2 is : beaks
Modified String 1 : ge
Modified String 2 : ba

Time complexity: O(n), where n is the length of the strings.
Auxiliary space: O(n), where n is the length of the strings, because we create a temporary list to store the filtered elements before joining them into a string.