14. Longest Common Prefix

 

Finding the Longest Common Prefix in JavaScript

When working with arrays of strings, a common problem is finding the longest common prefix among these strings. The longest common prefix is the initial portion of all strings in the array that is identical. This is a frequent problem on coding platforms like LeetCode, and it's essential to understand how to tackle it efficiently. In this blog post, we'll dive into the intuition, approach, and complexity of finding the longest common prefix in JavaScript.

Intuition

The intuition behind finding the longest common prefix is simple. By sorting the array of strings lexicographically (alphabetically), we can bring the smallest and largest strings to the beginning and end of the array. The common prefix between the first and last string in this sorted array will give us the longest common prefix for the entire array. This approach leverages the natural order of strings to simplify our task.

Approach

  1. Sort the Array: First, we sort the array of strings lexicographically. This step ensures that the strings with the smallest and largest prefixes come first and last.

    javascript
    strs.sort();

  2. Initialize Result Variable: We create a result string to store our common prefix.

    javascript
    let result = "";

  3. Determine the Length for Comparison: We find the minimum length between the first and last strings in the sorted array to ensure we don't compare beyond the length of the shortest string.

    javascript
    let n = Math.min(strs[0].length, strs[strs.length - 1].length);

  4. Compare Characters: We iterate through the characters of the first and last strings up to the determined length. If characters at any position differ, we return the current result. Otherwise, we append the matching character to the result.

    javascript
    for(let i = 0; i < n; i++) {
    if(strs[strs.length - 1].charAt(i) !== strs[0].charAt(i)) {
        return result;
    }
    result += strs[0].charAt(i);
}

  5. Return the Result: After the loop, we return the accumulated result, which represents the longest common prefix.

    javascript
    return result;

Complexity

  • Time Complexity: The time complexity of sorting the array is O(n log n), where n is the number of strings. Comparing the characters takes O(m) time, where m is the length of the shortest string. Therefore, the overall time complexity is O(n log n + m).

  • Space Complexity: The space complexity is O(1) because we only use a constant amount of extra space for the result variable and the loop counters.

Example Code

Here's the complete JavaScript code to find the longest common prefix among an array of strings:

javascript
strs.sort();
let result = "";
let n = Math.min(strs[0].length, strs[strs.length - 1].length);
for(let i = 0; i < n; i++) {
    if(strs[strs.length - 1].charAt(i) !== strs[0].charAt(i)) {
        return result;
    }
    result += strs[0].charAt(i);
}
return result;

Conclusion

This approach to finding the longest common prefix is both efficient and straightforward. By sorting the strings and focusing on the first and last elements, we can determine the common prefix shared by all strings in the array.

For more detailed explanations and additional solutions, check out my solution on LeetCode: Longest Common Prefix - LeetCode

We hope this guide helps you understand how to solve the longest common prefix problem using JavaScript. Happy coding! šŸš€

If you have any questions or need further clarification, feel free to ask in the comments below!

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