The weight distribution of a class of constacyclic codes

Let F-q be a finite field with q elements. For a non zero element lambda in F-q, we consider lambda-constacyclic codes of length N over F-q, where characteristic of F-q does not divide N. We find the necessary and sufficient conditions when a lambda-constacyclic codes of length N over F-q has generator polynomial of the form (x(n) - beta), beta in F-q. We explicitly determine the weight distribution of such lambda-constacyclic codes directly from their generator polynomials.