Count of numbers upto M with GCD equals to K when paired with M
Given two integers M and K, the task is to count the number of integers between [0, M] such that GCD of that integer with M equals to K.
Examples:
Input: M = 9, K = 1
Output: 6
Explanation:
The possible numbers such that when paired with 9, there GCD is 1, are 1, 2, 4, 5, 7, 8.Input: M = 10, K = 5
Output: 1
Approach:
- Integers having GCD K with M will be of the form K, 2K, 3K, …..and so on up to M.
- Let’s consider the coefficients of K i.e 1, 2, 3, 4…up to (M/K).
- Now we just have to find the count of such coefficients which have GCD with the number (M/K) = 1. So now problem reduces to find the number of integers between 1 to (M/K) having Gcd with (m/k) = 1.
- To find this we will use the Euler totient function of (M/K).
Below is the implementation of the above approach:
C++
// C++ program to Count of numbers// between 0 to M which have GCD// with M equals to K. #include <bits/stdc++.h>using namespace std; // Function to calculate GCD// using euler totient functionint EulerTotientFunction(int limit){ int copy = limit; // Finding the prime factors of // limit to calculate it's // euler totient function vector<int> primes; for (int i = 2; i * i <= limit; i++) { if (limit % i == 0) { while (limit % i == 0) { limit /= i; } primes.push_back(i); } } if (limit >= 2) { primes.push_back(limit); } // Calculating the euler totien // function of (m/k) int ans = copy; for (auto it : primes) { ans = (ans / it) * (it - 1); } return ans;} // Function print the count of// numbers whose GCD with M// equals to Kvoid CountGCD(int m, int k){ if (m % k != 0) { // GCD of m with any integer // cannot be equal to k cout << 0 << endl; return; } if (m == k) { // 0 and m itself will be // the only valid integers cout << 2 << endl; return; } // Finding the number upto which // coefficient of k can come int limit = m / k; int ans = EulerTotientFunction(limit); cout << ans << endl;}// Driver codeint main(){ int M = 9; int K = 1; CountGCD(M, K); return 0;} |
Java
// Java program to Count of numbers// between 0 to M which have GCD// with M equals to K.import java.util.*; class GFG{ // Function to calculate GCD// using euler totient functionstatic int EulerTotientFunction(int limit){ int copy = limit; // Finding the prime factors of // limit to calculate it's // euler totient function Vector<Integer> primes = new Vector<Integer>(); for (int i = 2; i * i <= limit; i++) { if (limit % i == 0) { while (limit % i == 0) { limit /= i; } primes.add(i); } } if (limit >= 2) { primes.add(limit); } // Calculating the euler totien // function of (m/k) int ans = copy; for (int it : primes) { ans = (ans / it) * (it - 1); } return ans;} // Function print the count of// numbers whose GCD with M// equals to Kstatic void CountGCD(int m, int k){ if (m % k != 0) { // GCD of m with any integer // cannot be equal to k System.out.print(0 +"\n"); return; } if (m == k) { // 0 and m itself will be // the only valid integers System.out.print(2 +"\n"); return; } // Finding the number upto which // coefficient of k can come int limit = m / k; int ans = EulerTotientFunction(limit); System.out.print(ans +"\n");} // Driver codepublic static void main(String[] args){ int M = 9; int K = 1; CountGCD(M, K); }} // This code is contributed by sapnasingh4991 |
Python3
# Python3 program to Count of numbers# between 0 to M which have GCD# with M equals to K. # Function to calculate GCD# using euler totient functiondef EulerTotientFunction(limit): copy = limit # Finding the prime factors of # limit to calculate it's # euler totient function primes = [] for i in range(2, limit + 1): if i * i > limit: break if (limit % i == 0): while (limit % i == 0): limit //= i primes.append(i) if (limit >= 2): primes.append(limit) # Calculating the euler totien # function of (m//k) ans = copy for it in primes: ans = (ans // it) * (it - 1) return ans # Function print the count of# numbers whose GCD with M# equals to Kdef CountGCD(m, k): if (m % k != 0): # GCD of m with any integer # cannot be equal to k print(0) return if (m == k): # 0 and m itself will be # the only valid integers print(2) return # Finding the number upto which # coefficient of k can come limit = m // k ans = EulerTotientFunction(limit) print(ans) # Driver codeif __name__ == '__main__': M = 9 K = 1 CountGCD(M, K) # This code is contributed by mohit kumar 29 |
C#
// C# program to Count of numbers// between 0 to M which have GCD// with M equals to K.using System;using System.Collections.Generic; class GFG{ // Function to calculate GCD// using euler totient functionstatic int EulerTotientFunction(int limit){ int copy = limit; // Finding the prime factors of // limit to calculate it's // euler totient function List<int> primes = new List<int>(); for (int i = 2; i * i <= limit; i++) { if (limit % i == 0) { while (limit % i == 0) { limit /= i; } primes.Add(i); } } if (limit >= 2) { primes.Add(limit); } // Calculating the euler totien // function of (m/k) int ans = copy; foreach (int it in primes) { ans = (ans / it) * (it - 1); } return ans;} // Function print the count of// numbers whose GCD with M// equals to Kstatic void CountGCD(int m, int k){ if (m % k != 0) { // GCD of m with any integer // cannot be equal to k Console.Write(0 + "\n"); return; } if (m == k) { // 0 and m itself will be // the only valid integers Console.Write(2 + "\n"); return; } // Finding the number upto which // coefficient of k can come int limit = m / k; int ans = EulerTotientFunction(limit); Console.Write(ans + "\n");} // Driver codepublic static void Main(String[] args){ int M = 9; int K = 1; CountGCD(M, K);}} // This code is contributed by PrinciRaj1992 |
Output:
6
Attention reader! Don’t stop learning now. Get hold of all the important mathematical concepts for competitive programming with the Essential Maths for CP Course at a student-friendly price. To complete your preparation from learning a language to DS Algo and many more, please refer Complete Interview Preparation Course.
