Implementing Levenshtein Distance in JavaScript

Introduction

In this lab, we will explore the Levenshtein Distance algorithm and its implementation in JavaScript. The purpose of this lab is to understand how to calculate the difference between two strings by measuring the minimum number of single-character edits (insertions, deletions, substitutions) required to transform one string into the other. By the end of this lab, you will have a solid understanding of the Levenshtein Distance algorithm and how to use it in your own JavaScript projects.

Levenshtein Distance Algorithm

To calculate the difference between two strings, you can use the Levenshtein distance algorithm. Here's how you can do it:

1. If either string has a length of zero, return the length of the other one.
2. Use a nested for loop to iterate over the letters of the target and source strings.
3. Calculate the cost of substituting the letters corresponding to i - 1 and j - 1 in the target and source respectively (0 if they are the same, 1 otherwise).
4. Use Math.min() to populate each element in the 2D array with the minimum of the cell above incremented by one, the cell to the left incremented by one, or the cell to the top left incremented by the previously calculated cost.
5. Return the last element of the last row of the produced array.

To start practicing this coding, open the Terminal/SSH and type node. Here's the code you can use:

const levenshteinDistance = (s, t) => {
  if (!s.length) return t.length;
  if (!t.length) return s.length;
  const arr = [];
  for (let i = 0; i <= t.length; i++) {
    arr[i] = [i];
    for (let j = 1; j <= s.length; j++) {
      arr[i][j] =
        i === 0
          ? j
          : Math.min(
              arr[i - 1][j] + 1,
              arr[i][j - 1] + 1,
              arr[i - 1][j - 1] + (s[j - 1] === t[i - 1] ? 0 : 1)
            );
    }
  }
  return arr[t.length][s.length];
};

console.log(levenshteinDistance("duck", "dark")); // 2

Summary

Congratulations! You have completed the Levenshtein Distance lab. You can practice more labs in LabEx to improve your skills.