JavaScript Coding Test Course, Radix Sort

This course will introduce the Radix Sort algorithm implemented in JavaScript and detail how to use it to solve coding test problems. We will systematically learn the concept of the Radix Sort algorithm, its implementation method, time complexity, and example problems.

What is Radix Sort?

Radix Sort is one of the sorting algorithms and an efficient method for sorting numbers with a similar number of digits. The key to this method is to sort the numbers by dividing them into individual digits (units, tens, etc.) and then sequentially considering the digits to sort the entire number.

The Principle of Radix Sort

Radix Sort proceeds in the following order:

  1. Find the maximum number of digits in the input array. This determines how many passes are needed to perform the sorting.
  2. Perform a stable sort for each digit, starting from the least significant digit (units) to the most significant digit (maximum digit).
  3. Finally, after all digit sorting is complete, the original array will be sorted.

Time Complexity

The time complexity of Radix Sort mainly depends on the stable sorting algorithm used, but it is generally O(nk), where n is the number of numbers to be sorted and k is the digit length of the largest number. Radix Sort can only be used for integers by nature, but it can also be applied in a modified version for characters or strings.

Implementing Radix Sort in JavaScript

Basic Algorithm Implementation

Below is an example code of Radix Sort implemented in JavaScript:

function getMax(array) {
    let max = array[0];
    for (let i = 1; i < array.length; i++) {
        if (array[i] > max) {
            max = array[i];
        }
    }
    return max;
}

function countingSort(array, place) {
    const n = array.length;
    const output = new Array(n);
    const count = new Array(10).fill(0);

    for (let i = 0; i < n; i++) {
        const digit = Math.floor(array[i] / place) % 10;
        count[digit]++;
    }

    for (let i = 1; i < 10; i++) {
        count[i] += count[i - 1];
    }

    for (let i = n - 1; i >= 0; i--) {
        const digit = Math.floor(array[i] / place) % 10;
        output[count[digit] - 1] = array[i];
        count[digit]--;
    }

    for (let i = 0; i < n; i++) {
        array[i] = output[i];
    }
}

function radixSort(array) {
    const max = getMax(array);
    for (let place = 1; Math.floor(max / place) > 0; place *= 10) {
        countingSort(array, place);
    }
    return array;
}

// Usage example
const numbers = [170, 45, 75, 90, 802, 24, 2, 66];
console.log(radixSort(numbers)); // Output: [2, 24, 45, 66, 75, 90, 170, 802]

Example Problem: Sorting an Integer Array

Now, let’s apply Radix Sort to a practical problem. The problem is as follows:

Problem: Given an array of integers, write a function to sort this array in ascending order using the Radix Sort algorithm.

Problem Approach

  1. Receive the input array as a function argument.
  2. Use the Radix Sort algorithm to sort the array.
  3. Return the sorted array.

Implementation and Testing

Based on the Radix Sort algorithm explained above, we can implement a function to solve the problem as follows:

function sortIntegers(array) {
    return radixSort(array);
}

// Test
const testArray = [5, 3, 8, 1, 2, 7, 4, 6];
console.log(sortIntegers(testArray)); // Output: [1, 2, 3, 4, 5, 6, 7, 8]

Conclusion

In this course, we learned about the Radix Sort algorithm and how to implement it in JavaScript. Radix Sort is very efficient for sorting large integers, especially showing excellent performance for numbers with fewer digits. Utilizing Radix Sort to approach various coding test problems will be a very beneficial experience. I hope you make good use of the concepts and implementation methods of Radix Sort in your upcoming coding tests.