C# this is with basic knowledge

public static List rotLeft(List a, int d) {

        int length=a.Count()-1;
        int[] newArr = new int[length+1];

        for(int i = length;i>-1;i--){

            if(i-d<0)
            {                   
                int j=i-d;                   
                newArr[length+1+j]=a[i];                      
            }
            else
            {
                newArr[i-d]=a[i];
            }
        }
        return   newArr.ToList() ;
}

}