Puzzling Addiction

This is a very clever jigsaw sudoku puzzle. The regions of the puzzles are shaped like US states, and the given letters are the state abbreviations. I wrote a quick program to solve the puzzle. My program isn't that smart. It only uses "single candidate", "single position" and "guessing" techniques to solve the puzzle. A smarter problem would use some other techniques.

Solving it manually, I was able to use some other techniques (naked triple, candidate line, forcing chains, etc.) to solve it. I'd be interested to see if anyone can come up with a solution that doesn't use forcing chains or nishio. I consider both of these a form of guessing and not very elegant.

Here's the program: Download file

Here's the output of the program: Download file