From 06d70b2ce83bf5cbe2650cec8313c297ed475072 Mon Sep 17 00:00:00 2001
From: Akshat2806 <akshat.0542@gmail.com>
Date: Fri, 2 Oct 2020 12:03:36 +0530
Subject: [PATCH] ETF Sieve implementation

---
 General/ETF_sieve.cpp | 45 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 General/ETF_sieve.cpp

diff --git a/General/ETF_sieve.cpp b/General/ETF_sieve.cpp
new file mode 100644
index 0000000..73e2790
--- /dev/null
+++ b/General/ETF_sieve.cpp
@@ -0,0 +1,45 @@
+//Time complexity-O(loglog(n))
+#include<iostream> 
+using namespace std;
+
+#define ll long long int
+
+
+void ETF(int n) 
+{ 
+
+	ll phi[n+1]; 
+	for (int i=1; i<=n; i++) 
+		phi[i] = i; //initialize all array elements with indices 
+
+
+	for (int p=2; p<=n; p++) 
+	{ 
+		//if phi[p] ==p implies phi[p] is not calculated and it is prime
+		if (phi[p] == p) 
+		{ 
+			//etf of prime p=p-1
+			phi[p] = p-1; 
+
+			
+			for (int i = 2*p; i<=n; i += p) 
+			{ 
+			//calculating from the formula
+			phi[i] = (phi[i]/p) * (p-1); 
+			} 
+		} 
+	} 
+
+	// Printing phi values 
+	for (int i=1; i<=n; i++) 
+	cout << "Totient of " << i << " is "
+		<< phi[i] << endl; 
+} 
+
+// Driver program to test above function 
+int main() 
+{ 
+	int n = 10; 
+	ETF(n); 
+	return 0; 
+}