Merge pull request #3 from cinfinit/master

Primality Test C++

Author: Phantsure

PrimalityTest/c++/primality.cpp

@@ -0,0 +1,53 @@
+#include <iostream>
+using namespace std;
+// following are the very basic approaches
+
+//method 1
+/*
+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; 
+}
+*/
+ //Time complexity of this solution is O(n)
+ 
+ 
+ 
+ //method 2
+ 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; 
+} 
+//Time complexity of this solution is O(underroot n)
+
+int main(void){
+// to check whether n is prime or not 
+int n ; 
+//taking input from the user 
+cin>>n; 
+
+isPrime(n) ? cout<<"The number is prime ":cout<<"Number is not prime ";
+
+return 0;
+
+}