Merge pull request matthewsamuel95#73 from 96mohitm/segmented-sieve

Added Segmented sieve in cpp

Author: matthewsamuel95

Math/sieve_of_eratosthenes/SegmentedSieve.cpp

@@ -0,0 +1,75 @@
+// print all primes smaller than
+// n using segmented sieve
+#include <bits/stdc++.h>
+using namespace std;
+void simpleSieve(int limit, vector<int> &prime)
+{
+
+    bool mark[limit+1];
+    memset(mark, true, sizeof(mark));
+ 
+    for (int p=2; p*p<limit; p++)
+    {
+        
+        if (mark[p] == true)
+        {
+
+            for (int i=p*2; i<limit; i+=p)
+                mark[i] = false;
+        }
+    }
+ 
+    for (int p=2; p<limit; p++)
+    {
+        if (mark[p] == true)
+        {
+            prime.push_back(p);
+            cout << p << "  ";
+        }
+    }
+}
+ 
+void segmentedSieve(int n)
+{
+    int limit = floor(sqrt(n))+1;
+    vector<int> prime;  
+    simpleSieve(limit, prime); 
+ 
+    int low  = limit;
+    int high = 2*limit;
+ 
+    while (low < n)
+    {
+        
+        bool mark[limit+1];
+        memset(mark, true, sizeof(mark));
+ 
+        for (int i = 0; i < prime.size(); i++)
+        {
+            
+            int loLim = floor(low/prime[i]) * prime[i];
+            if (loLim < low)
+                loLim += prime[i];
+ 
+            for (int j=loLim; j<high; j+=prime[i])
+                mark[j-low] = false;
+        }
+ 
+        for (int i = low; i<high; i++)
+            if (mark[i - low] == true)
+                cout << i << "  ";
+ 
+        low  = low + limit;
+        high = high + limit;
+        if (high >= n) high = n;
+    }
+}
+ 
+int main()
+{
+    int n = 100;
+    cout << "Primes smaller than " << n << ":n ";
+    segmentedSieve(n);
+    cout<<"\n";
+    return 0;
+}