Permutations of capitalization

Question

I want to build a list containing every possible permutation of capitalization of a word. so it would be

List permutate(string word)
{
    List         


        

Answer 1

If order doesn't matter, you can try Linq. We enumerate all binary numbers in a range of [0..2**word.Length]. and treat each number as mask: 0 - lower case, 1 - upper case. For instance for happy we have

mask      string
----------------
00000  ->  happy
00001      Happy
00010      hAppy
00011      HAppy
00100      haPpy
00101      HaPpy
...
11111      HAPPY

Code:

  using System.Linq;

  ... 

  List permutate(string word) =>
    Enumerable
      .Range(0, 1 << word.Length)
      .Select(mask => string.Concat(word.Select((c, i) => (mask & (1 << i)) == 0 
         ? char.ToLower(c) 
         : char.ToUpper(c))))
      .ToList();

Demo:

  Console.Write(string.Join(", ", permutate("happy")));

Outcome:

happy, Happy, hAppy, HAppy, haPpy, HaPpy, hAPpy, HAPpy, hapPy, HapPy, hApPy, HApPy, haPPy, HaPPy, hAPPy, HAPPy, happY, HappY, hAppY, HAppY, haPpY, HaPpY, hAPpY, HAPpY, hapPY, HapPY, hApPY, HApPY, haPPY, HaPPY, hAPPY, HAPPY