Swift Coding Test Course, Arrays and Lists

In this course, we will address algorithm problems using arrays and lists with the Swift programming language. An array is a data structure that can hold multiple pieces of data of the same type, while a list is a structure that stores data in a contiguous block of memory. Understanding the properties of arrays and lists can greatly assist in solving various algorithm problems.

Problem Description

Problem 1: Intersection of Two Arrays

Write a function to find the common elements and compute the intersection of the two given arrays. The arrays may have duplicate elements, and the resulting array should not include duplicate elements.

For example, let’s assume we are given the following two arrays.

let array1 = [1, 2, 3, 4, 5]
let array2 = [4, 5, 6, 7, 8]

In this case, the output of the function should be [4, 5].

Problem Solving Process

Problem Analysis

To approach this problem, we need to think of an algorithm to compare the elements of the two arrays to find the common ones. A basic approach would be to iterate through both arrays using a loop to find common elements. However, this method could lead to a time complexity of O(n^2), which may reduce performance. Therefore, we should use a more efficient method.

Efficient Approach

To enhance efficiency, we can utilize sets. A set is a data structure that allows each element to be stored uniquely, providing fast search performance. Here is a summary of the solution process.

  1. Convert the first array into a set. This has a time complexity of O(n).
  2. Iterate through the second array while checking for existence in the set. This also has a time complexity of O(m).
  3. Create a new array to store the common elements and return the result.

Code Implementation

Below is the Swift code written using the above approach.

func intersection(array1: [Int], array2: [Int]) -> [Int] {
    var set = Set(array1) // Convert the first array into a set
    var result = [Int]() // An array to hold the result
    
    for element in array2 {
        if set.contains(element) { // Check if the element from the second array is in the set
            result.append(element) // If it is, add it to the result array
            set.remove(element) // Remove from the set to avoid duplicates
        }
    }
    
    return result
}

// Example execution
let array1 = [1, 2, 3, 4, 5]
let array2 = [4, 5, 6, 7, 8]
let result = intersection(array1: array1, array2: array2)
print(result) // Output: [4, 5]

Time Complexity Analysis

Analyzing the time complexity of the above solution, converting the first array into a set takes O(n), and iterating through the second array takes O(m). Therefore, the total time complexity is O(n + m). This method is much more efficient than the existing O(n^2) method.

Problem Variations

By modifying the original problem, if the elements of the arrays are sorted, we can further improve the performance of the solution by utilizing binary search. Searching for elements in a sorted array can enhance performance to O(log n). Additionally, if you are familiar with the concept of binary search, you can utilize it to improve search speed.

Conclusion

In this course, we have solved the problem of finding the intersection of two arrays using arrays and lists. Understanding and utilizing arrays and lists, which are fundamental data structures in programming, is crucial. Continue to tackle various algorithm problems to enhance your skills.

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