Swift Coding Test Course, Let's try DDR

Hello, everyone! Today we will tackle an algorithm problem implemented in Swift. The topic is an algorithmic problem that arises in the ‘DDR (Dance Dance Revolution)’ game. This problem will be very useful for improving your understanding of Swift programming and algorithms. Let’s explain the problem first and then solve it together.

Problem Description

The problem is as follows:

Problem: DDR Pattern Analysis

In the DDR game, players score points by stepping on the arrows that appear on the screen. Each arrow appears at 1-second intervals, and when a pattern is given, write an algorithm to calculate how many arrows can be accurately stepped on within the given time.

The following information will be provided as input:

n: Total number of arrows (1 ≤ n ≤ 1000)
t: Given time (seconds, 1 ≤ t ≤ 100)
Pattern array: An array listing the activation times of each arrow (each item is 1 ≤ item ≤ t)

Write a program that calculates and outputs how many arrows can be stepped on within the given time based on the input pattern.

Example Input

5 3
1 2 3 4 5

Example Output

Solution Process

Now let’s approach the problem step by step. Follow the processes below to understand the solution method.

Step 1: Input Handling

First, we need to read the number of arrows, the time limit, and the activation times of the arrows given in the input. The input data will be stored in an array. For example, in Swift, you can do the following:

import Foundation

// Input handling
let input = readLine()!.split(separator: " ").map { Int($0)! }
let n = input[0]  // Total number of arrows
let t = input[1]  // Given time (seconds)
let arrows = readLine()!.split(separator: " ").map { Int($0)! } // Arrow activation times

Step 2: Understanding the Problem

The task is to find out how many arrows can be stepped on within the given time ‘t’. In other words, we need to count the number of arrows in the arrow arrangement array from 1 to t seconds.

Step 3: Sorting the Array and Validating

After receiving the input, we need to sort the arrow activation time array. This will simplify the counting based on valid time.

let sortedArrows = arrows.sorted()

Step 4: Writing the Counting Logic

Now we simply need to count the number of arrows that satisfy the conditions. The method for counting how many arrows correspond to the given time ‘t’ is very straightforward. We can increment the count each time we encounter an arrow that is less than or equal to t while traversing the array.

var count = 0
for arrow in sortedArrows {
    if arrow <= t {
        count += 1
    } else {
        break // No need to check further
    }
}

Step 5: Output the Result

After checking all the arrows, we print the count to the console.

print(count)

Complete Code

By integrating all the above steps, we can write a program as follows:

import Foundation

// Input handling
let input = readLine()!.split(separator: " ").map { Int($0)! }
let n = input[0]  // Total number of arrows
let t = input[1]  // Given time (seconds)
let arrows = readLine()!.split(separator: " ").map { Int($0)! } // Arrow activation times

// Sorting the arrows
let sortedArrows = arrows.sorted()

// Count variable
var count = 0
for arrow in sortedArrows {
    if arrow <= t {
        count += 1
    } else {
        break
    }
}

// Output the result
print(count)

Conclusion

Thus, we have solved the DDR arrow counting problem using Swift. Algorithm problems can initially seem difficult, but it is important to organize the problem well and approach it step by step. Keep practicing various problems and enhance your Swift programming skills! Thank you!

Swift Coding Test Course, Let’s try DDR