Codeforces 110A: Lucky Number Problem Solution in C++

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Codeforces problem 110A requires us to determine whether a given number is lucky or not. A lucky number is defined as a number that contains only the digits 4 and 7, and the total count of these digits is either 4 or 7.

To solve this problem, we need to first read the input number. We can then loop through each digit of the number and check if it is a 4 or a 7. We can do this by using the modulo operator (%) to get the remainder of the number when divided by 10, which gives us the rightmost digit of the number. If the digit is a 4 or a 7, we increment a counter variable.

After we have counted the number of 4s and 7s in the input number, we can check if the count is either 4 or 7. If it is, then the number is lucky, and we output “YES”. Otherwise, the number is not lucky, and we output “NO”.

Here’s the complete code in C++:

#include <iostream>

using namespace std;

int main()
{
    long long number;
    cin >> number;
    int count = 0;
    while (number != 0)
    {
        if (number % 10 == 4 || number % 10 == 7)
        {
            count += 1;
        }
        number /= 10;
    }
    if (count == 4 || count == 7)
    {
        cout << "YES" << endl;
    }
    else
    {
        cout << "NO" << endl;
    }
    return 0;
}

In conclusion, the above code solves Codeforces problem 110A by counting the number of 4s and 7s in a given input number and checking if the count is either 4 or 7.

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