I saw this problem in Steven Skiena's book, The Algorithm Design Manual. Below is my solution in C++:

vector<int> rotateLeft(int d, vector<int> arr) {
    int n = arr.size();

    vector<int> a(n);
    for(int i=0; i<n; i++) {
        a[i] = arr[(i+d)%n];
    }
    
    return a;
}

public static List<Integer> rotateLeft(int d, List<Integer> arr) {
       List<Integer> results = new ArrayList<>(arr);
for(int i=arr.size()-1;i>=0;i--){
    int index = (i-d);
    if(index<0){
         index = index+ arr.size();
        results.set(index, arr.get(i));
    } else {
        results.set(index, arr.get(i));
    }
}
return results;
}

}

For Python Users:

def rotateLeft(d, arr):
    # Write your code here
    newarr=[]
    w = n-d
    for i in range(len(arr)):
        rev = arr[i-w]
        newarr.append(rev)

return newarr

My solution:

def rota(d,arr):
    s = arr[0:d].copy()
    del arr[0:d]
    arr.extend(s)
    
    return arr

C# Solution - Basically you want to first convert List to Array type cuz you want to use range operator which makes it easy to dissect arrays. Lastly you want to append those two arrays and convert it back to list.

 var x = arr.ToArray();
        int[] a = x[..d];
        int[] b = x[d..];
        List<int> c = new []{ b, a}.SelectMany(s => s).ToList();
        return c;