segemented sieve

Number Theory/segmented_sieve.cpp

@@ -0,0 +1,49 @@
+#define MAX_N 33000
+bool is_prime[MAX_N];
+
+bool is_sieve_eval = false;
+
+void sieve_erathosis(){
+	if( is_sieve_eval ) return;
+	is_sieve_eval = true;
+	memset(is_prime,false,sizeof(is_prime));
+	is_prime[0] = true , is_prime[1] = true;
+	for(int num = 2 ; num*num < MAX_N ; num++ ){
+		if( !is_prime[num] ){
+			for(int val = num*num ; val < MAX_N ; val += num ){
+				is_prime[val] = true;
+			}
+		}
+	}
+}
+
+vector<bool> seg_prime;
+
+void segmented_sieve(int m,int n){
+    
+    seg_prime.resize(n-m+1,false);
+ 
+    if( m == 1 ){
+        seg_prime[0] = true;
+    }
+ 
+    int sz = ceil(sqrt(n));
+ 
+    int factor = 0;
+    for(int i = 2 ; i < sz ; i++ ){
+        if( !is_prime[i]){
+            factor = ceil((1.0*m)/i);
+            for(int num = (factor==1?2:factor) * i ; num < n + 1 ; num += i ){
+                seg_prime[num-m] = true;
+            }
+        }
+    }
+ 
+    for(int i = 0 ; i < n-m+1 ; i++ ){
+        if( !seg_prime[i] )
+            cout << i+m << '\n';
+    }
+    cout << '\n';
+ 
+    seg_prime.clear();
+}