What is the Longest Common Prefix in Strings?

The concept of the longest common prefix is an interesting and often discussed topic in technical interviews. A common interview question may ask you to find the longest common prefix among a group of strings. This problem not only tests your understanding of strings but also your algorithmic skills.

To summarize, the longest common prefix of a set of strings is the longest string that is a prefix of all the strings in that set. A prefix, in this context, means that the initial segment of the string matches across all strings being evaluated.

For example, consider the strings ["flower", "flow", "flight"]. In this case, the longest common prefix would be "fl", as it is the longest string that appears at the beginning of each of the provided strings.

Breaking Down the Problem

When faced with this question, it can be helpful to think of a few approaches. Here are three commonly used methods to find the longest common prefix:

1. Horizontal scanning: Compare the first string with the next one, keeping track of the common prefix, and then continue this way through all the strings.

2. Vertical scanning: Compare characters of the strings index by index until mismatches are found.

3. Divide and conquer: Split the set of strings into halves to find the longest common prefix in each half, and then merge the results.

Let’s write some code for the horizontal scanning method, as it is straightforward and easy to understand.

Code Example: Horizontal Scanning

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Explanation of the Code

1. Edge Case Handling: The function first checks if the list of strings is empty. If it is, it immediately returns an empty string since there are no prefixes to find.

2. Initializing the Prefix: The variable prefix is initialized to the first string in the list, which acts as a starting point.

3. Iterating Through Strings: The code then iterates over each string in the list starting from the second string.

4. Finding the Common Prefix: Inside the loop, it checks whether the current string starts with the prefix. If it does not, the code shortens the prefix by one character at a time.

5. Return Result: If the prefix becomes empty, it returns an empty string since that indicates there is no common prefix. If all strings are processed, it returns the final prefix.

Example Usage

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Using this approach ensures you correctly find the longest common prefix efficiently. When preparing for interviews, practicing problems like these can sharpen your problem-solving skills and prepare you for various scenarios you may encounter.