AlgoBreath

Longest Common Prefix

The Longest Common Prefix (LCP) problem is a classic problem in computer science and string processing. The core idea is to find the longest substring that is a prefix of all strings in a given set. Let's break this down:

  1. String: A string is a sequence of characters. For example, "apple" is a string.

  2. Prefix: A prefix of a string is any leading part of it. For example, "app" is a prefix of "apple".

  3. Longest Common Prefix: In a set of strings, the longest common prefix is the longest string that is a prefix of every string in the set. For instance, if we have the strings "interspace", "interstellar", and "interstate", their longest common prefix is "inters".

The importance of solving the LCP problem is evident in various fields such as bioinformatics (for DNA sequence analysis), data compression, and text processing.

Algorithmic Approach

The most straightforward way to find the LCP is to compare the characters of the strings in the set one by one. Here's a general approach:

  1. Identify the Shortest String: The LCP cannot be longer than the shortest string in the set.

  2. Compare Characters: Starting from the first character, compare the corresponding character of each string. Continue until the characters do not match in all strings.

  3. Return the LCP: The matched characters up to the point of mismatch form the Longest Common Prefix.

Example in Python

Let's write a Python function to implement this:

def longest_common_prefix(strs):
    # Check if the list is empty
    if not strs:
        return ""
    
    # Find the shortest string in the list
    shortest = min(strs, key=len)

    # Initialize the LCP as an empty string
    lcp = ""

    # Iterate over the characters of the shortest string
    for i in range(len(shortest)):
        # Check if this character is present at the same position in all strings
        if all(s[i] == shortest[i] for s in strs):
            lcp += shortest[i]  # Append the character to LCP
        else:
            break  # Stop if any character doesn't match

    return lcp

# Example usage
strings = ["flower", "flow", "flight"]
print(longest_common_prefix(strings))  # Output: "fl"

In this code:

  • We first handle the edge case where the input list might be empty.
  • We find the shortest string to limit our comparison.
  • We iterate over each character of the shortest string, checking if that character is the same in the corresponding position of all strings.
  • If the characters match, we add them to the LCP. If not, we break the loop as no longer prefix is possible.

This is a basic approach and works well for a small number of relatively short strings. For larger datasets or more complex requirements, more sophisticated algorithms may be needed.

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