Euler Totient Function (Seive)

Number Theory/EulerTotientFunction.cpp

@@ -0,0 +1,32 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+using ll = long long;
+
+const ll MAXN = 1000001;
+int t;
+ll n, phi[MAXN];
+
+void seive() {
+    for (ll i = 1; i < MAXN; i++) phi[i] = i;
+
+    for (ll i = 2; i < MAXN; i++) {
+        if (phi[i] == i) {
+            phi[i] = phi[i] - 1;
+            for (ll j = i * 2; j < MAXN; j += i) {
+                phi[j] = phi[j] - (phi[j] / i);
+            }
+        }
+    }
+}
+
+int main() {
+    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
+
+    seive();
+    cin >> t;
+    while (t--) {
+        cin >> n;
+        cout << phi[n] << "\n";
+    }
+}