Added optimized prime number finder in range 0-n

c++/prime-numbers-between-0-n.cpp

@@ -0,0 +1,37 @@
+// https://practice.geeksforgeeks.org/problems/find-prime-numbers-in-a-range/0
+
+#include <iostream>
+using namespace std;
+void solve_test()
+{
+   long long n;
+   cin>>n; // taking the value till we want to get the primes
+   vector<bool> prime(n+1 , true); //intializing a vector of bool with all initial value true
+   prime[0] = false; //marking 0 and 1 non-primes
+   prime[1] = false;
+   for(int i=2;i<=n;i++){
+    //if a number is prime then we are marking its multiples as prime
+    if(prime[i]){
+        for(int j=i+i;j<=n;j+=i)
+        prime[j] = false;
+    }
+   }
+   //printing all the prime that are true in the vector
+   for(int i=0;i<=n;i++){
+    if(prime[i])
+    cout<<i<<" ";
+   }
+   cout<<endl;
+   //TC = O(log(log(n))) + O(n)
+   //SC = O(n)
+}
+
+int main()
+{
+    int t; 
+    cin >> t; 
+
+    while(t--)
+        solve_test();
+	return 0;
+}

c++/prime-numbers-in-range.cpp

@@ -15,7 +15,6 @@ bool isPrime(unsigned long int n)
     }
     return true; 
 }
-
 void solve_test()
 {
     unsigned long int a , b, number;