Consider the following sorted array of integers:

Our goal is to count the number of unique values in this array, which in this case is 5. To accomplish this, we can use a two-pointer algorithm that iterates through the array and updates the values in place.

Let’s walk through the uniquevalue function to see how this works

The uniquevalue function takes an array arr as an input and initializes the first pointer i to 0. It then iterates through the array with a second pointer j, comparing the values at the two pointers. If the values are different, the function increments i and updates the value at the new index to the value at j. If the values are the same, the function does nothing.

After iterating through the entire array, the value of i represents the index of the last unique value. Since array indices start at 0, we add 1 to i to get the total number of unique values.

Conclusion

In this blog post, we learned how to count the number of unique values in a sorted array using a two-pointer algorithm in JavaScript. This algorithm updates the array in place, making it an efficient solution to this problem. By understanding this algorithm, you can easily apply it to other programming languages and data structures.