"""
    permutation(n, r)
        
    returns the number of ways to choose r items from n items
    with order and without repetition

# Arguments:
- `n`: Positive integers of items to choose from
- 'r': Positive integers of items to choose

Contributed By:- [Mayur Dahibhate](https://github.com/mayurdahibhate)
"""

function permutation(n, r)

    function factorial(n)        
        fact = 1
        
        if n == 0 || n == 1
            return fact
        end
         
        for i = 1:n
            fact = fact * i
        end 
        
        return fact
    end
    
    perm = factorial(n) / factorial(n - r) 

    return convert(Int64, perm)
end