Global variable "count" ambiguous

The problem is all because of the second line here:

#include <algorithm>
using namespace std;

The line using namespace std brings all the names from <algorithm> which also has a function called count, and in your code, you've declared a variable count. Hence the ambiguous error.

The solution is to never write using namespace std. It is bad bad bad.

Instead, use std::cout, std::cin, std::endl, std::count and so on, in your code.

I think I may have figured this out. I have found that removing the using namespace std doesn't help, but when I change the name of the variable to something which is less common, like count can be changed to cnt or some personal versions like knt or isCycle. I don't exactly know what is the reason behind this.