Codeforces 110A Nearly Lucky Number Solution & Explanation

Difficulty : 800

Problem Description

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Unfortunately, not all numbers are lucky. Petya calls a number nearly lucky if the number of lucky digits in it is a lucky number. He wonders whether number n is a nearly lucky number.

Input

The only line contains an integer n (1 ≤ n ≤ 10¹⁸).

Please do not use the %lld specificator to read or write 64-bit numbers in С++. It is preferred to use the cin, cout streams or the %I64d specificator.

Output

Print on the single line “YES” if n is a nearly lucky number. Otherwise, print “NO” (without the quotes).

Eamples

Solution

We can use an integer to count the occurrences of lucky numbers in the input string, and by iterating through the input string, we can easily solve this problem.

C# Solution

Solution1

string word = Console.ReadLine();
int cnt = 0;

foreach(var c in word){
    if(c=='4' || c=='7')
    {
        cnt+=1;
    }
}

Console.WriteLine((cnt==4 || cnt ==7) ? "YES" : "NO");

Java Solution

Solution1

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String word = scanner.nextLine();
        int cnt = 0;
        
        for (char c : word.toCharArray()) {
            if(c=='4' || c=='7')
            {
                cnt+=1;
            }
        }
        
        System.out.print((cnt==4 || cnt ==7) ? "YES" : "NO");
        
    }
}

Python3 Solution

Solution1

word = input()
cnt = 0

for c in word:
    if(c=='4' or c=='7'):
        cnt+=1
       
print( "YES" if (cnt==4 or cnt==7) else "NO" )

Conclusion

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The problem link : Problem – 110A – Codeforces

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