Edit Distance


In this section we will try to solve a problem mentioned in Perl Weekly Challenge. The problem is called Edit Distance.

You are given two strings str1 and str2. Write a function to find out the minimum operations required to convert str1 into str2. The operations can be insert, remove or replace a character.


Input: str1 = "kitten"; str2 = "sitting"
Output: 3

Operation 1: replace 'k' with 's'
Operation 2: replace 'e' with 'i'
Operation 3: insert 'g' at the end
Input: str1 = "sunday"; str2 = "monday"
Output: 2

Operation 1: replace 's' with 'm'
Operation 2: replace 'u' with 'o'


Let’s look at the code now. We will iterate till the length of the smaller string. We will check if the characters are same – if they are not we will increment the counter. Then at the end of the iteration we will add the difference between the two string lengths.

private static int editDistance(String s1, String s2) {
    int len = s1.length();
    if (s2.length() < s1.length()) {
        len = s2.length();
    int count = 0;
    for (int i = 0; i < len; i++) {
        if (s1.charAt(i) != s2.charAt(i)) {
    return count + Math.abs(s1.length() - s2.length());

Let’s now see a Kotlin version of the same solution

private fun editDistance(s1: String, s2: String): Int {
    var len = s1.length
    if (s2.length < s1.length) {
        len = s2.length
    var count = 0
    for (i in 0 until len) {
        if (s1[i] != s2[i]) {
    return count + Math.abs(s1.length - s2.length)


In this article we saw how to solve the edit distance problem in Java and Kotlin.

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