Swift Coding Test Course, Picking Up Pebbles

Hello, everyone! Today we will take an in-depth look at the coding test problem ‘Stone Removal’ using Swift. This problem is useful for laying the foundation of algorithms and is frequently featured in practical exams. In this post, we will explain the problem description, solution approach, Swift code, and detail the problem-solving process step by step.

Problem Description

Let’s assume a game of removing stones from a given array. Each element of the array represents the number of stones. In each turn, the player can remove a required number of stones, with the goal of removing all the stones. However, the rules for removing stones are as follows:

  • The player must remove at least one stone in each turn.
  • The maximum number of stones that can be removed in each turn must be equal to or less than the number of stone piles.

The objective of this game is to determine the minimum number of turns required to remove all the stones. Through this problem, you can practice algorithmic thinking and Swift syntax.

Approach

To solve this problem, we need to traverse each element of the given array and calculate the total number of turns. The problem can be solved using a loop. The main steps can be summarized as follows.

  1. Sum the number of stones from the array.
  2. To calculate the total number of turns, divide the number of stones by the maximum number that can be removed per turn.
  3. If there’s a remainder, an additional turn must be added.

Now, let’s write the Swift code.

Swift Code


func minimumTurns(to collectStones stones: [Int]) -> Int {
    // Calculate the total number of stones
    let totalStones = stones.reduce(0, +)
    
    // Calculate available turns
    let turns = totalStones / stones.count
    let remainder = totalStones % stones.count
    
    // Add an extra turn if there’s a remainder
    return remainder == 0 ? turns : turns + 1
}

// Test example
let stones = [3, 5, 2, 6]
let result = minimumTurns(to: collectStones: stones)
print("Minimum number of turns: \(result)")

Problem-Solving Process

The above code first uses the `reduce` function on the stone array to calculate the total number of stones. Next, it divides by the size of the array to compute the average number of turns. If there is a remainder, it adds 1 to the base number of turns to return the final number of turns.

Example Analysis

Let’s examine the case where the stone array is [3, 5, 2, 6]. First, the total sum of the stones is:

3 + 5 + 2 + 6 = 16

Since the number of stones is 4, the average number of turns is:

16 / 4 = 4

Since there is no remainder, the minimum number of turns is 4.

Conclusion

In this lecture, we covered the process of solving the ‘Stone Removal’ problem using Swift. By understanding the rules of the problem and implementing an algorithm to calculate the optimal number of turns, you can improve your algorithmic thinking. Don’t forget to continue practicing basic algorithm problems like this while preparing for coding tests. In the next lecture, we will tackle more complex algorithm problems. Thank you!