Permutation of an array, with repetition, in Java

Question

There are some similar questions on the site that have been of some help, but I can\'t quite nail down this problem, so I hope this is not repetitive.

This is a home

Answer 1

Here is c# version to generate the permutations of given string with repetitions:

(essential idea is - number of permutations of string of length 'n' with repetitions is n^n).

string[] GetPermutationsWithRepetition(string s)
        {
            s.ThrowIfNullOrWhiteSpace("s");
            List permutations = new List();
            this.GetPermutationsWithRepetitionRecursive(s, "",
                permutations);
            return permutations.ToArray();
        }
        void GetPermutationsWithRepetitionRecursive(string s, string permutation, List permutations)
        {
            if(permutation.Length == s.Length)
            {
                permutations.Add(permutation);
                return;
            }
            for(int i =0;i

Below are the corresponding unit tests:

[TestMethod]
        public void PermutationsWithRepetitionTests()
        {
            string s = "";
            int[] output = { 1, 4, 27, 256, 3125 };
            for(int i = 1; i<=5;i++)
            {
                s += i;
                var p = this.GetPermutationsWithRepetition(s);
                Assert.AreEqual(output[i - 1], p.Length);
            }
        }