Javascript Coding Test Course, Let’s Try DDR

Problem Description

Here is a simple version of the DDR game. The game proceeds in the following format.

The user must press the corresponding keys based on the four arrows shown below:

• ↑ (Up)
• ↓ (Down)
• ← (Left)
• → (Right)

The goal of the game is to score points by accurately pressing the keys in the order of the given arrow inputs. If a wrong arrow is pressed, the user loses points.

You need to write a function that receives user input and calculates the score when given n arrows. This function adds 1 point for each correct input matching the answer sequence and subtracts 1 point for each incorrect input.

Input Format

        - Arrow array: ["↑", "↓", "←", "→"]
        - User input array: ["↑", "↑", "←", "→", "↓"]
        

Output Format

Returns the user’s final score.

Problem Solving Process

To solve this problem, let’s first design the algorithm. The steps to solve the problem are as follows.

1. Declare the arrow array and user input array.
2. Initialize a variable to maintain the score.
3. Iterate over user inputs and compare each input with the correct answers.
4. If the input is correct, increase the score by 1; if incorrect, decrease it by 1.
5. After checking all inputs, return the final score.

Now that the algorithm is clear, let’s write the code.

Code Implementation

function calculateScore(correctArrows, userArrows) {
    let score = 0;

    for (let i = 0; i < userArrows.length; i++) {
        if (userArrows[i] === correctArrows[i]) {
            score += 1; // Correct
        } else {
            score -= 1; // Incorrect
        }
    }

    return score; // Return final score
}

// Example usage
const correctArrows = ["↑", "↓", "←", "→"];
const userArrows = ["↑", "↑", "←", "→", "↓"];

const finalScore = calculateScore(correctArrows, userArrows);
console.log("Final score is:", finalScore);
        

Code Explanation

Let’s explain the code step by step.

1. Function Definition

The function calculateScore takes the arrow array and user input array as parameters. It initializes the score variable to 0 for score calculation.

2. Checking with Loop

Using a for loop, we iterate through the user input array. We check if each user’s input matches the correct arrows.

If they match, we add 1 point; if they do not match, we subtract 1 point.

3. Return Final Score

After checking all user inputs, we return the score value. This value is the final score.

Code Testing

To verify that the code works correctly, let’s create some test cases.

Test Case 1

const correct1 = ["↑", "↓", "←", "→"];
const user1 = ["↑", "↓", "←", "→"];

console.log("Test Case 1 - Score:", calculateScore(correct1, user1)); // 4
        

Test Case 2

const correct2 = ["↑", "↓", "←", "→"];
const user2 = ["↑", "↑", "←", "→", "↓"];

console.log("Test Case 2 - Score:", calculateScore(correct2, user2)); // 2
        

Test Case 3

const correct3 = ["↑", "↓", "←", "→"];
const user3 = ["→", "→", "→", "→"];

console.log("Test Case 3 - Score:", calculateScore(correct3, user3)); // -4
        

Conclusion

In this article, we solved a basic algorithm problem of the DDR game using JavaScript. We were able to solidify the basics of JavaScript through basic problem-solving methods and code writing.

This simple algorithm problem is one of the common types of problems that appear in interviews. Therefore, it’s beneficial to solve many similar problems and develop your own coding style. Thank you!