Find the Longest Common Suffix in a List of Strings

Finding the longest common suffix within a list of strings is a common task in programming, particularly useful in areas like data processing and file management. This post will explore efficient Python methods to solve this problem, providing clear explanations and code examples.

Understanding the Problem

The goal is to identify the longest string that appears at the end of every string in a given list. For instance, if the input list is ["flowerpower", "superpower", "waterpower"], the longest common suffix is “power”. If there’s no common suffix, the result should be an empty string.

Method 1: Iterative Approach

This approach iterates through the strings from the end, comparing characters at each position. It’s straightforward and easy to understand.

def longest_common_suffix_iterative(strings):
    """
    Finds the longest common suffix of a list of strings using an iterative approach.

    Args:
        strings: A list of strings.

    Returns:
        The longest common suffix string.  Returns an empty string if no common suffix exists.
    """
    if not strings:
        return ""

    shortest_string = min(strings, key=len)  # Start with the shortest string
    suffix = ""
    for i in range(len(shortest_string) - 1, -1, -1):
        char = shortest_string[i]
        is_common = all(string[i] == char for string in strings) #check if character at index 'i' is common to all strings
        if is_common:
            suffix = char + suffix # add the common character to the beginning of the suffix
        else:
            break  # Stop if a character is not common

    return suffix


strings1 = ["flowerpower", "superpower", "waterpower"]
print(f"Longest common suffix of {strings1}: {longest_common_suffix_iterative(strings1)}")  # Output: power

strings2 = ["apple", "banana", "orange"]
print(f"Longest common suffix of {strings2}: {longest_common_suffix_iterative(strings2)}")  # Output: 

strings3 = ["coding", "codingisfun", "codingisawesome"]
print(f"Longest common suffix of {strings3}: {longest_common_suffix_iterative(strings3)}") # Output: coding

strings4 = []
print(f"Longest common suffix of {strings4}: {longest_common_suffix_iterative(strings4)}") #Output: ""

Method 2: Using os.path.commonprefix (for prefixes, adaptable for suffixes)

The os.path.commonprefix function is designed to find the common prefix. We can adapt it to find the common suffix by reversing the strings.

import os

def longest_common_suffix_os(strings):
    """Finds the longest common suffix using os.path.commonprefix on reversed strings."""
    if not strings:
        return ""
    reversed_strings = [s[::-1] for s in strings]
    common_prefix = os.path.commonprefix(reversed_strings)
    return common_prefix[::-1]

strings1 = ["flowerpower", "superpower", "waterpower"]
print(f"Longest common suffix of {strings1}: {longest_common_suffix_os(strings1)}")  # Output: power

strings2 = ["apple", "banana", "orange"]
print(f"Longest common suffix of {strings2}: {longest_common_suffix_os(strings2)}")  # Output: 

Both methods effectively solve the problem. The iterative approach offers more control and might be slightly more efficient for very large lists, while the os.path.commonprefix method provides a concise and readable solution. The choice depends on your priorities and coding style.

Handling Edge Cases

The code examples above handle empty input lists gracefully, returning an empty string. Consider adding error handling for other potential edge cases, such as input that is not a list of strings, in a production environment.