Python: Find the longest common ending between two given strings

Last update on April 17 2025 13:00:47 (UTC/GMT +8 hours)

Longest Common Ending

Write a Python program to find the longest common ending between two given strings.

Sample Solution-1:

Python Code:

# Define a function 'test' that takes two strings as input.
def test(str1, str2):
    # Iterate through the indices of the second string.
    for i in range(len(str2)):
        # Check if a substring of the second string starting from index 'i' is present at the end of the first string,
        # and if the last characters of both strings match.
        while str2[i:] in str1 and str2[-1] == str1[-1]:
            # If the conditions are met, return the common ending substring.
            return str2[i:]
    
    # If no common ending is found, return an empty string.
    return ""

# Test case 1
str1_1 = "running"
str2_1 = "ruminating"
print("Original strings: " + str1_1 + "  " + str2_1)
print("Common ending between said two strings: " + test(str1_1, str2_1))

# Test case 2
str1_2 = "thisisatest"
str2_2 = "testing123testing"
print("\nOriginal strings: " + str1_2 + "  " + str2_2)
print("Common ending between said two strings: " + test(str1_2, str2_2))

Sample Output:

Original strings: running  ruminating
Common ending between said two strings: ing

Original strings: thisisatest  testing123testing
Common ending between said two strings:

Explanation:

Here is a breakdown of the above Python code:

test Function:

The "test()" function takes two strings as input.
It iterates through the indices of the second string (str2).
For each index 'i', it checks if a substring of 'str2' starting from index i is present at the end of 'str1', and if the last characters of both strings match.
If these conditions are met, it returns the common ending substring.
If no common ending is found, it returns an empty string.

Flowchart:

Sample Solution-2:

Python Code:

# Define a function 'test' that takes two strings as input.
def test(str1, str2):
    # Continue removing the first character of str2 until it becomes a suffix of str1.
    while not str1.endswith(str2):
        str2 = str2[1:]
    
    # Return the common ending between str1 and str2.
    return str2

# Test case 1
str1_1 = "running"
str2_1 = "ruminating"
print("Original strings: " + str1_1 + "  " + str2_1)
print("Common ending between said two strings: " + test(str1_1, str2_1))

# Test case 2
str1_2 = "thisisatest"
str2_2 = "testing123testing"
print("\nOriginal strings: " + str1_2 + "  " + str2_2)
print("Common ending between said two strings: " + test(str1_2, str2_2))

Sample Output:

Original strings: running  ruminating
Common ending between said two strings: ing

Original strings: thisisatest  testing123testing
Common ending between said two strings:

Explanation:

Here is a breakdown of the above Python code:

test Function:

The "test()" function takes two strings as input.
It uses a while loop to repeatedly remove the first character of 'str2' until 'str2' becomes a suffix of 'str1'.
When the loop condition (not str1.endswith(str2)) is 'False', the function returns the common ending between 'str1' and 'str2'.

Flowchart:

For more Practice: Solve these Related Problems:

Write a Python program to find the longest common suffix between two strings by comparing characters from the end.
Write a Python program to determine the common ending substring of two input strings.
Write a Python program to reverse both strings and compute the longest common prefix of the reversed strings.
Write a Python program to extract and return the longest common ending shared by two given strings.

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Python Code Editor:

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