Given a range **L** to **R**, the task is to find the highest occurring digit in prime numbers lie between L and R (both inclusive). If multiple digits have same highest frequency print the largest of them. If no prime number occurs between L and R, output -1.

Examples:

Input :L = 1 and R = 20.Output :1 Prime number between 1 and 20 are 2, 3, 5, 7,11,13,17,19. 1 occur maximum i.e 5 times among 0 to 9.

The idea is to start from L to R, check if the number is prime or not. If prime then increment the frequency of digits (using array) present in the prime number. To check if number is prime or not we can use Sieve of Eratosthenes.

Below is the implementation of this approach:

## C++

// C++ program to find the highest occurring digit // in prime numbers in a range L to R. #include<bits/stdc++.h> using namespace std; // Sieve of Eratosthenes void sieve(bool prime[], int n) { for (int p = 2; p * p <= n; p++) { if (prime[p] == false) for (int i = p*2; i <= n; i+=p) prime[i] = true; } } // Returns maximum occurring digits in primes // from l to r. int maxDigitInPrimes(int L, int R) { bool prime[R+1]; memset(prime, 0, sizeof(prime)); // Finding the prime number up to R. sieve(prime, R); // Initialse frequency of all digit to 0. int freq[10] = { 0 }; int val; // For all number between L to R, check if prime // or not. If prime, incrementing the frequency // of digits present in the prime number. for (int i = L; i <= R; i++) { if (!prime[i]) { int p = i; // If i is prime while (p) { freq[p%10]++; p /= 10; } } } // Finding digit with highest frequency. int max = freq[0], ans = 0; for (int j = 1; j < 10; j++) { if (max <= freq[j]) { max = freq[j]; ans = j; } } return ans; } // Driven Program int main() { int L = 1, R = 20; cout << maxDigitInPrimes(L, R) << endl; return 0; }

## Java

// Java program to find the highest occurring digit // in prime numbers in a range L to R. import java.util.Arrays; class GFG { // Sieve of Eratosthenes static void sieve(boolean prime[], int n) { for (int p = 2; p * p <= n; p++) { if (prime[p] == false) for (int i = p * 2; i <= n; i += p) prime[i] = true; } } // Returns maximum occurring digits in primes // from l to r. static int maxDigitInPrimes(int L, int R) { boolean prime[] = new boolean[R + 1]; Arrays.fill(prime, false); // Finding the prime number up to R. sieve(prime, R); // Initialse frequency of all digit to 0. int freq[] = new int[10]; int val; // For all number between L to R, check if // prime or not. If prime, incrementing // the frequency of digits present in the // prime number. for (int i = L; i <= R; i++) { if (!prime[i]) { int p = i; // If i is prime while (p > 0) { freq[p % 10]++; p /= 10; } } } // Finding digit with highest frequency. int max = freq[0], ans = 0; for (int j = 1; j < 10; j++) { if (max <= freq[j]) { max = freq[j]; ans = j; } } return ans; } // Driver code public static void main(String[] args) { int L = 1, R = 20; System.out.println(maxDigitInPrimes(L, R)); } } // This code is contributed by Anant Agarwal.

## C#

// C# program to find the highest // occurring digit in prime numbers // in a range L to R. using System; class GFG { // Sieve of Eratosthenes static void sieve(bool []prime, int n) { for (int p = 2; p * p <= n; p++) { if (prime[p] == false) for (int i = p * 2; i <= n; i += p) prime[i] = true; } } // Returns maximum occurring digits // in primes from l to r. static int maxDigitInPrimes(int L, int R) { bool []prime = new bool[R + 1]; for(int i = 0; i < R+1; i++) prime[i] = false; // Finding the prime number up to R. sieve(prime, R); // Initialse frequency of all digit to 0. int []freq = new int[10]; // For all number between L to R, check if // prime or not. If prime, incrementing // the frequency of digits present in the // prime number. for (int i = L; i <= R; i++) { if (!prime[i]) { int p = i; // If i is prime while (p > 0) { freq[p % 10]++; p /= 10; } } } // Finding digit with highest frequency. int max = freq[0], ans = 0; for (int j = 1; j < 10; j++) { if (max <= freq[j]) { max = freq[j]; ans = j; } } return ans; } // Driver code public static void Main() { int L = 1, R = 20; Console.Write(maxDigitInPrimes(L, R)); } } // This code is contributed by nitin mittal.

Output:

1

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