'commit'

GESP/Level5/new.cpp

@@ -0,0 +1,24 @@
+//欧拉筛
+const int N = 1e5 + 10;
+int primes[N], cnt;     // primes[]存储所有素数
+bool st[N];             // st[x]存储x是否被筛掉
+void get_primes(int n) {
+    for (int i = 2; i <= n; i++) {
+        if (!st[i]) primes[cnt++] = i;
+        for (int j = 0; primes[j]*i <= n; j++) {
+            st[primes[j] * i] = true;
+            if (i % primes[j] == 0) break;
+        }
+    }
+}
+void get_primes(int n){
+  for (int i = 2;i<=n;i++){
+    if(!st[i])
+      primes[cnt++] = i;
+    for (int j = 0; primes[j] * i <= n;j++){
+      st[primes[j] * i] = true;
+      if(i%primes[j]==0)
+        break;
+    }
+  }
+}