Merge pull request #369 from ishikasinha-d/Sieve-of-Eratosthenes

Create Sieve-of-Eratosthenes.c++

Author: smv1999

Numbers/Sieve-of-Eratosthenes.cpp

@@ -0,0 +1,41 @@
+// Sieve of Eratosthenes 
+//time complexity = O(n* log(logn))
+
+#include<bits/stdc++.h>
+#define fast ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);
+using namespace std;
+typedef long long int ll;
+const ll N= 10e6;
+vector<bool> Prime(N+1,true);
+using namespace std;
+
+void sieve(){
+    ll i,j;
+    Prime[0]=Prime[1]=false;
+
+    //adding this otpimization will reduce n/2 computations
+    //since even no.s are not prime
+    for(i=2;i<N+1;i+=2)
+        Prime[i]=false;
+
+    for(i=2;i<N+1;i++)
+    {
+        if(Prime[i])
+            for(j=i*i;j<N+1;j+=i)
+            if(Prime[j])
+                Prime[j]=false;
+    }
+}
+
+int main()
+{ 
+   fast;
+
+ll i;
+sieve();
+for(i=1;i<100;i++)
+    if(Prime[i])
+        cout<<i<<" ";
+return 0;
+
+}