XY-Chain comparator Bug, @PseudoFish fix

[1to9only]

To import PseudoFish XY-Chain Bug Fix where a comparator bug leading to a crash while attempting to solve certain puzzles using XY-Chains.

XY-Chain Bug, to recreate:

• Paste this grid:

  5.2.8..4.93..64.........93.....7.6.9..6....58.....62...7..9....4....38....3.5...7

• IllegalArgumentException:

  Exception in thread "Thread-9" java.lang.IllegalArgumentException: Comparison method violates its general contract!
      at java.util.ComparableTimSort.mergeLo(ComparableTimSort.java:744)
      at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:481)
      at java.util.ComparableTimSort.mergeForceCollapse(ComparableTimSort.java:422)
      at java.util.ComparableTimSort.sort(ComparableTimSort.java:222)
      at java.util.Arrays.sort(Arrays.java:1312)
      at java.util.Arrays.sort(Arrays.java:1506)
      at java.util.ArrayList.sort(ArrayList.java:1464)
      at java.util.Collections.sort(Collections.java:143)
      at solver.ChainSolver.getXYChains(ChainSolver.java:251)
      at solver.ChainSolver.getStep(ChainSolver.java:176)
      at solver.SudokuStepFinder.getStep(SudokuStepFinder.java:265)
      at solver.SudokuSolver.getHint(SudokuSolver.java:465)
      at solver.SudokuSolver.solve(SudokuSolver.java:238)
      at solver.SudokuSolver.solve(SudokuSolver.java:175)
      at solver.SudokuSolver.solve(SudokuSolver.java:161)
      at sudoku.SolverProgressDialog.run(SolverProgressDialog.java:120)
      at java.lang.Thread.run(Thread.java:748)

[1to9only]

The fix is to uncomment these lines in SolutionStep.java:

2010,2014c2010,2014
< //            // change 20110512: short chains first!
< //            int chainDiff = compareChainLengths(o);
< //            if (chainDiff != 0) {
< //                return chainDiff;
< //            }
---
>             // change 20110512: short chains first!
>             int chainDiff = compareChainLengths(o);
>             if (chainDiff != 0) {
>                 return chainDiff;
>             }

However, those lines were commented out by hobiwan a long time ago to fix an ALS-Chains sorting problem, see here.

Commits on Mar 31, 2012
Fixed: #3513603: Search for all steps ignores ALS types
fixed a problem with sorting: ALS-Chains were sometimes sorted incorrectly

So fixing this issue will likely bring back the old ALS-Chains sorting problem!!