Add : Project Euler #1 Multiples of 3 and 5 (Hackerrank)

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get  3,5,6,and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below n.

Author: deepakgarg0802

Project Euler 1.cpp

@@ -0,0 +1,30 @@
+#include <iostream>
+#include <algorithm>
+
+using namespace std;
+
+long long sum_n(long long n,long long d)
+{
+    long long x= (n*(n+1)*d) /2;
+    return x;
+}    
+    
+int main(){
+    int t;
+    long long ans,temp,x,y,z;
+    cin >> t;
+    for(int a0 = 0; a0 < t; a0++){
+        int n;
+        cin >> n;
+        n--;
+        temp= (n-(n%3))/3;
+        x= sum_n(temp,3);
+        temp= (n-(n%5))/5;
+        y= sum_n(temp,5);
+        temp= (n-(n%15))/15;
+        z=sum_n(temp,15);
+        //cout<<x<<" ";cout<<y<<" ";cout<<z<<" ";
+        cout<<x+y-z<<endl;
+    }
+    return 0;
+}