Slide pieces on the board so that they reach the given end configuration.
- Identify which arrangement of pieces can be slided to form the given configuration. (from WPC 2017)
- Identify the minimum number of swaps required to achieve the given configuration. The swapped tiles need not be adjacent to each other. (from WPC 2017)
History of the puzzle
Most famous and earliest of sliding puzzles, the 15 puzzle, was invented by Noyes Palmer Chapman (USA) in 1874. The game was already popular in America in the 1880s. 
Since then, many variants have emerged. To name a few, Klotski was patented by Lewis W. Hardy (USA) in 1909. On-Off puzzle by Nob Yoshigahara (Japan) was used in a single-puzzle round in WPC 1992.
Appearances in the past WPCs
- WPC 2017/Round 17 by Amit Sowani, Swaroop Guggilam