Add the Lin-Kernighan heuristic for the TSP

[crlgb]

Dear contributors,

I am currently working on my Bachelor's thesis, wherein I compare several TSP algorithms on the data provided in the 2021 Amazon Last Mile Research Challenge. I have found, that contrary to the exposure in academia, the Lin-Kernighan (LK) heuristic has not been implemented as part of JGraphT. LK is, on most instances, more performant than Christofides and would therefore be worthy of an implementation is this library.

• DOI: 10.1287/opre.21.2.498
  • Lin, S. / Kernighan, B. W.; An Effective Heuristic Algorithm for the Traveling-Salesman Problem; 1973-04
• DOI: 10.1016/s0377-2217(99)00284-2
  • Helsgaun, Keld; An effective implementation of the Lin–Kernighan traveling salesman heuristic; 2000-10