Swift Coding Test Course, Dictionary Lookup

1. Problem Definition

Recently, the importance of coding tests in IT companies has increased, requiring the ability to solve various algorithm problems.
In this course, we will explore algorithm problem-solving using the Swift programming language through the “Word Finder” problem.
This problem involves finding the position of a specific word in a given list of words, requiring an understanding of basic data structures and algorithms.

Problem Description

This problem is to find a specific word in a given list and output its index number.
For example, given the following list of words:

        Word list: ["apple", "banana", "cherry", "date", "fig", "grape"]
        Word to find: "cherry"
        

In this case, the index of “cherry” is 2. If the word to find is not in the list, it should return -1.

2. Problem Analysis

To solve this problem, it is common to iterate through the given list of words and compare it with the target word.
However, to handle it more efficiently, we can utilize the binary search algorithm.
Binary search is a method used to effectively find a specific value in sorted data, reducing time complexity to O(log n).

Sorting the List

First, the list of words must be sorted to use binary search.
Therefore, we will sort the given list of words before applying binary search.

3. Algorithm Design

The algorithm consists of the following steps:

1. Sort the word list.
2. Use binary search to find the specific word.
3. Return the found index or -1 if it does not exist.

4. Code Implementation

Now, let’s implement the above algorithm using Swift.

        import Foundation

        func binarySearch(words: [String], target: String) -> Int {
            var low = 0
            var high = words.count - 1

            while low <= high {
                let mid = (low + high) / 2
                if words[mid] == target {
                    return mid
                } else if words[mid] < target {
                    low = mid + 1
                } else {
                    high = mid - 1
                }
            }
            return -1
        }

        func findWordIndex(words: [String], target: String) -> Int {
            let sortedWords = words.sorted()
            return binarySearch(words: sortedWords, target: target)
        }

        // Example
        let words = ["apple", "banana", "cherry", "date", "fig", "grape"]
        let target = "cherry"
        let index = findWordIndex(words: words, target: target)
        print("Index number: \(index)") // Result: Index number: 2
        

5. Code Explanation

The above code consists of the following steps:

• binarySearch function:

  Searches for the target word in the provided list using binary search.
  It adjusts the current search interval with the low and high variables and calculates the mid index for comparison.
  If the searching word matches, it returns the corresponding index; otherwise, it narrows the search interval.

• findWordIndex function:

  This function sorts the list of words and then calls binary search.
  It returns the index of the word to find.

6. Time Complexity

The time complexity of this algorithm can be divided into two parts.
First, the sorting of the word list is O(n log n).
Secondly, the binary search part is O(log n).
Therefore, the overall time complexity can be evaluated as O(n log n).

7. Various Test Cases

To enhance the accuracy of the algorithm, various test cases can be created.
For example:

Test Case 1

        Input: ["apple", "banana", "cherry", "date"], "banana"
        Output: 1
        

Test Case 2

        Input: ["apple", "banana", "cherry", "date"], "kiwi"
        Output: -1
        

Test Case 3

        Input: [], "apple"
        Output: -1
        

You can run several test cases to check if the algorithm works correctly.

8. Conclusion and Further Learning

In this course, we explored the algorithmic problem-solving method using Swift through the “Word Finder” problem.
Coding tests are an important process to assess understanding of algorithms and data structures, so practicing various problems is beneficial.
Also, consider using the BLS (Best Learning Strategy) principle to repetitively learn algorithms and improve your skills.

Additionally, solving problems on platforms like LeetCode and HackerRank is also a good way to improve algorithm problem-solving skills.
This will help you acquire the skills required in actual coding tests and will be beneficial for job preparation as well.

Thank you!