https://www.codewars.com/kata/558dd9a1b3f79dc88e000001/javascript
Find The Duplicated Number in a Consecutive Unsorted List | Codewars
You are given an array of n+1 integers 1 through n. In addition there is a single duplicate integer. The array is unsorted. An example valid array would be [3,...
in aunsorted listfindduplicatednumber