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Prime Triplet in C++
In this problem, we are given a number N. Our task is to print all prime triplets less than N.
Prime triplet is a set of three prime numbers. That are of the form (p, p+2, p+6) or (p, p+4, p+6). All prime numbers are grouped according to the above triplets as every third prime in the direct pattern is a multiple of 6.
Let’s see an example to understand the problem
Input: N = 13 Output: 5 7 11
To solve this problem, we have to find all prime numbers less than equal to N. And the check for triplets.
The code to show the implementation of our solution,
Example
#include <bits/stdc++.h>
using namespace std;
void findPrimes(int n, bool prime[]) {
for (int p = 2; p * p <= n; p++) {
if (prime[p] == true) {
for (int i = p * 2; i <= n; i += p)
prime[i] = false;
}
}
}
void printPrimeTriplets(int n) {
bool prime[n + 1];
memset(prime, true, sizeof(prime));
findPrimes(n, prime);
for (int i = 2; i <= n-6; ++i) {
if (prime[i] && prime[i + 2] && prime[i + 6])
cout<<i<<"\t"<<(i+2)<<"\t"<<(i+6)<<endl;
else if (prime[i] && prime[i + 4] && prime[i + 6])
cout<<i <<"\t"<<(i + 4)<<"\t"<<(i + 6)<<endl;
}
}
int main() {
int N = 15;
cout<<"Prime Triplets Less than "<<N<<" are :\n";
printPrimeTriplets(N);
return 0;
}Output
Prime Triplets Less than 15 are : 5 7 11 7 11 13
Updated on: 03-Feb-2020
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