15 puzzle solver/Optimal solution
Solution in 31 moves: u2r2d3ru2ld2ru3ld3l2u3r2d2l2dru3rd3l2u2r3dl3dru2r2d2
original: move 1:u2 move 2:r2 move 3:d3 move 4:r move 5:u2 move 6:l move 7:d2 15 14 1 6 14 1 6 14 1 6 14 1 4 6 14 1 4 6 14 1 4 6 14 1 4 6 14 1 4 6 9 11 4 12 15 11 4 12 15 11 4 12 15 11 7 12 15 11 7 12 15 11 7 15 11 7 15 11 5 7 10 7 3 9 10 7 3 9 10 7 3 9 10 5 3 9 10 5 3 9 10 5 12 9 10 5 12 9 10 2 12 13 8 5 2 13 8 5 2 13 8 5 2 13 8 2 13 8 2 13 8 2 3 13 8 2 3 13 8 3 move 8:r move 9:u3 move 10:l move 11:d3 move 12:l2 move 13:u3 move 14:r2 move 15:d2 14 1 4 6 14 1 4 14 1 4 14 1 5 4 14 1 5 4 1 5 4 1 5 4 1 5 2 4 15 11 5 7 15 11 5 6 15 11 5 6 15 11 2 6 15 11 2 6 14 11 2 6 14 11 2 6 14 11 3 6 9 10 2 12 9 10 2 7 9 10 2 7 9 10 3 7 9 10 3 7 15 10 3 7 15 10 3 7 15 10 7 13 8 3 13 8 3 12 13 8 3 12 13 8 12 13 8 12 9 13 8 12 9 13 8 12 9 13 8 12 move 16:l2 move 17:d move 18:r move 19:u3 move 20:r move 21:d3 move 22:l2 move 23:u2 1 5 2 4 1 5 2 4 1 5 2 4 1 2 4 1 2 4 1 2 3 4 1 2 3 4 1 2 3 4 14 11 3 6 14 11 3 6 14 11 3 6 14 5 3 6 14 5 3 6 14 5 10 6 14 5 10 6 5 10 6 15 10 7 9 15 10 7 9 15 10 7 9 11 10 7 9 11 10 7 9 11 8 7 9 11 8 7 14 11 8 7 9 13 8 12 13 8 12 13 8 12 13 15 8 12 13 15 8 12 13 15 12 13 15 12 9 13 15 12 move 24:r3 move 25:d move 26:l3 move 27:d move 28:r move 29:u2 move 30:r2 move 31:d2 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 5 10 6 5 10 6 7 5 10 6 7 5 10 6 7 5 10 6 7 5 6 7 5 6 7 5 6 7 8 14 11 8 7 14 11 8 14 11 8 9 14 11 8 9 14 11 8 9 10 11 8 9 10 11 8 9 10 11 12 9 13 15 12 9 13 15 12 9 13 15 12 13 15 12 13 15 12 13 14 15 12 13 14 15 12 13 14 15