欧拉函数带模的部分和

D.cpp

@@ -0,0 +1,47 @@
+#include <bits/stdc++.h>
+using namespace std;
+vector<int>phi;
+void genPhi(int max){
+    int minDiv[max];
+    for(int i = 1; i < max; i++){
+        minDiv[i] = i;
+    }
+    for(int i = 2; i * i < max; i++){
+        if(minDiv[i] == i){
+            for(int j = i*i; j < max; j += i){
+                minDiv[j] = i;
+            }
+        }
+    }
+    phi[1] = 1;
+    for(int i = 2; i < max; i++){
+        phi[i] = phi[i / minDiv[i]];
+        if((i / minDiv[i]) % minDiv[i] == 0){
+            phi[i] *= minDiv[i];
+        }else{
+            phi[i] *= minDiv[i] - 1;
+        }
+    }
+}
+const int MAXN = 1000001;
+long long g[MAXN];
+int f[MAXN];
+int main(){
+//    ofstream cout("output.txt");
+    phi.resize(MAXN);
+    genPhi(MAXN);
+    for(int i = 1; i <= MAXN; i+=2){
+        f[i] = phi[i]%(i+1);
+    }
+    g[0] = 0;
+    for(int i = 1; i <= MAXN; i++){
+        g[i] = g[i-1] + f[i];
+    }
+    int T;
+    cin >> T;
+    for(int t = 1; t <= T; t++){
+        int n;
+        cin >> n;
+        cout << "Case "<<t<<": "<<g[n]<<endl;
+    }
+}