BitCounting https://www.codewars.com/kata/526571aae218b8ee490006f4;
NonRepeatingChar https://www.codewars.com/kata/52bc74d4ac05d0945d00054e;
SumStrAsNum https://www.codewars.com/kata/5324945e2ece5e1f32000370;
Permutation https://www.codewars.com/kata/5254ca2719453dcc0b00027d/train/csharp