rearrange the characters of a string so that any two adjacent characters are not the same

Question

How to rearrange the characters of a string so that any two adjacent characters are not the same? using c# c# Without using Hashmaps and Dictionary I managed to find each element of the string, and the occurrence of each element. This is what I've done so far

Answer 1

Using LINQ, you can gather the characters of the string, group them by duplicate characters, then pivot the groups and join then back into a string.

First, some extension methods to make Join easier:

public static class IEnumerableExt {
    public static string Join(this IEnumerable<char> chars) => String.Concat(chars); // faster >= .Net Core 2.1
    public static string Join(this IEnumerable<string> strings) => String.Concat(strings);
}

Then, an extension method to pivot an IEnumerable<IEnumerable<T>>:

public static class IEnumerableIEnumerableExt {
    public static IEnumerable<IEnumerable<T>> Pivot<T>(this IEnumerable<IEnumerable<T>> src) {
        var enums = src.Select(ie => ie.GetEnumerator()).ToList();
        var hasMores = Enumerable.Range(0, enums.Count).Select(n => true).ToList();

        for (; ; ) {
            var oneGroup = new List<T>();
            var hasMore = false;
            for (int j1 = 0; j1 < enums.Count; ++j1) {
                if (hasMores[j1]) {
                    hasMores[j1] = enums[j1].MoveNext();
                    hasMore = hasMore || hasMores[j1];
                    if (hasMores[j1])
                        oneGroup.Add(enums[j1].Current);
                }
            }

            if (!hasMore)
                break;

            yield return oneGroup;
        }

        for (int j1 = 0; j1 < enums.Count; ++j1)
            enums[j1].Dispose();
    }
}

Finally, use these to solve your problem:

var s = "How to rearrange the characters of a string";

var tryAns = s.OrderBy(c => c)
              .GroupBy(ch => ch)
              .Pivot()
              .Select(gch => gch.Join())
              .Join();

var dupRE = new Regex(@"(.)\1", RegexOptions.Compiled);
var hasDups = dupRE.IsMatch(tryAns);

// tryAns will be " Hacefghinorstw aceghnorst aeort aert ar r "
// hasDups will be false

If the resulting string has two adjacent identical characters, then hasDups will be true.