add files from section2 geekforgeeks

geekForgeeks/section2_number_theory/primeNumber.cpp

@@ -0,0 +1,14 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+int isPrime(int N) {
+
+    if(N <= 1)
+        return 0;
+
+    for(int i=2; i*i<=N; ++i)
+        if(N%i==0)
+            return 0;
+
+    return 1;
+}

geekForgeeks/section2_number_theory/sieveOfEratosthenes.cpp

@@ -0,0 +1,20 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+vector<int> sieveOfEratosthenes(int N){
+
+    vector<int> sieve(N,1);
+    vector<int> ans;
+    sieve[0] = sieve[1] = 0;
+
+    for(int i = 2; i < N; ++i) {
+        if(sieve[i] == 1) {
+            ans.push_back(i);
+            for(int j = i+i; j < N; j+=i)
+                sieve[j] = 0;
+        }
+    }
+
+    return ans;
+
+}