sieve of eratosthenes

sieve of eratosthenes

@@ -0,0 +1,54 @@
+#include<iostream>
+#include<cmath>
+using namespace std;
+
+
+void find_primes(bool sieve[], unsigned long long int size)
+{
+    // by definition 0 and 1 are not prime numbers
+    sieve[0] = false;
+    sieve[1] = false;
+
+    // all numbers <= max are potential candidates for primes
+    for (unsigned int i = 2; i <= size; ++i)
+    {
+        sieve[i] = true;
+    }
+
+    // loop through the first prime numbers < sqrt(max) (suggested by the algorithm)
+    unsigned int first_prime = 2;
+    for (unsigned int i = first_prime; i <= std::sqrt(double(size)); ++i)
+    {
+        // find multiples of primes till < max
+        if (sieve[i] = true)
+        {
+            // mark as composite: i^2 + n * i
+            for (unsigned int j = i * i; j <= size; j += i)
+            {
+                sieve[j] = false;
+            }
+        }
+    }
+}
+void print_primes(bool sieve[], unsigned long long int size)
+{
+    // all the indexes of the array marked as true are primes
+    for (unsigned long long int i = 0; i <= size; ++i)
+    {
+        if (sieve[i] == true)
+        {
+            std::cout << i <<" ";
+        }
+    }
+}
+//TIME COMPLEXITY-O(nlog(log(n)))
+//SPACE COMPLEXITY-O(n)
+
+int main(){
+unsigned long long int n;
+cin>>n;
+bool sieve[n];
+find_primes(sieve,n);
+print_primes(sieve,n);
+return 0;
+}