C++ Program to check Prime Number
Given a positive integer, check if the number is prime or not. A prime is a natural number greater than 1 that has no positive divisors other than 1 and itself. Examples of first few prime numbers are {2, 3, 5,
Examples:
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Input: n = 11 Output: true Input: n = 15 Output: false Input: n = 1 Output: false
// A school method based C++ program to check if a// number is prime#include <bits/stdc++.h>using namespace std; bool isPrime(int n){ // Corner case if (n <= 1) return false; // Check from 2 to n-1 for (int i = 2; i < n; i++) if (n % i == 0) return false; return true;} // Driver Program to test above functionint main(){ isPrime(11) ? cout << " true\n" : cout << " false\n"; isPrime(15) ? cout << " true\n" : cout << " false\n"; return 0;} |
Output:
true false
Time complexity of this solution is O(n)
Optimized School Method
// A optimized school method based C++ program to check// if a number is prime#include <bits/stdc++.h>using namespace std; bool isPrime(int n){ // Corner cases if (n <= 1) return false; if (n <= 3) return true; // This is checked so that we can skip // middle five numbers in below loop if (n % 2 == 0 || n % 3 == 0) return false; for (int i = 5; i * i <= n; i = i + 6) if (n % i == 0 || n % (i + 2) == 0) return false; return true;} // Driver Program to test above functionint main(){ isPrime(11) ? cout << " true\n" : cout << " false\n"; isPrime(15) ? cout << " true\n" : cout << " false\n"; return 0;} |
Output:
true false
Please refer complete article on Primality Test | Set 1 (Introduction and School Method) for more details!
