Python: Find the longest common ending between two given strings

Last update on May 24 2025 10:48:47 (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 Basic Exercises Home ↩
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Python Code Editor:

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