3-6-9 in Python

The 3-6-9 game is a popular counting game where players replace certain numbers with a special word. In this Python implementation, we create a list from 1 to n, but replace numbers that are multiples of 3 or contain the digits 3, 6, or 9 with the string "clap".

Problem Statement

Given a number n, construct a list with each number from 1 to n as strings, except when the number is a multiple of 3 or contains the digits 3, 6, or 9 − replace these with "clap".

For example, if the input is 20, the output will be: ['1', '2', 'clap', '4', '5', 'clap', '7', '8', 'clap', '10', '11', 'clap', 'clap', '14', 'clap', 'clap', '17', 'clap', 'clap', '20']

Algorithm

To solve this problem, we follow these steps −

• Create a list of numbers from 1 to n as strings

• For each number in the list:

  • If the number is divisible by 3, replace with "clap"

  • If the number contains digit '3', replace with "clap"

  • If the number contains digit '6', replace with "clap"

  • If the number contains digit '9', replace with "clap"

• Return the modified list

Implementation

class Solution:
    def solve(self, n):
        replacement = "clap"
        numbers = [str(i) for i in range(1, n + 1)]
        
        for i in range(len(numbers)):
            if int(numbers[i]) % 3 == 0:
                numbers[i] = replacement
            elif '3' in numbers[i]:
                numbers[i] = replacement
            elif '6' in numbers[i]:
                numbers[i] = replacement
            elif '9' in numbers[i]:
                numbers[i] = replacement
                
        return numbers

# Test the solution
solution = Solution()
result = solution.solve(20)
print(result)

['1', '2', 'clap', '4', '5', 'clap', '7', '8', 'clap', '10', '11', 'clap', 'clap', '14', 'clap', 'clap', '17', 'clap', 'clap', '20']

Optimized Version

We can simplify the condition checking by combining digit checks ?

def three_six_nine(n):
    result = []
    
    for i in range(1, n + 1):
        num_str = str(i)
        
        # Check if multiple of 3 or contains 3, 6, or 9
        if i % 3 == 0 or any(digit in num_str for digit in ['3', '6', '9']):
            result.append("clap")
        else:
            result.append(num_str)
    
    return result

# Test with different values
print("n = 15:", three_six_nine(15))
print("n = 10:", three_six_nine(10))

n = 15: ['1', '2', 'clap', '4', '5', 'clap', '7', '8', 'clap', '10', '11', 'clap', 'clap', '14', 'clap']
n = 10: ['1', '2', 'clap', '4', '5', 'clap', '7', '8', 'clap', '10']

How It Works

Let's trace through some examples to understand the logic ?

• Number 3: 3 % 3 == 0 (multiple of 3) ? "clap"

• Number 6: 6 % 3 == 0 (multiple of 3) ? "clap"

• Number 13: Contains digit '3' ? "clap"

• Number 16: Contains digit '6' ? "clap"

• Number 19: Contains digit '9' ? "clap"

• Number 11: Not multiple of 3, no forbidden digits ? "11"

Conclusion

The 3-6-9 game implementation checks each number for two conditions: being a multiple of 3 or containing the digits 3, 6, or 9. The optimized version uses Python's any() function for cleaner code and better readability.