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Take care of some edge cases in the backtracker

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This commit is contained in:
Eryn Wells 2017-10-11 20:25:11 -07:00
parent a9a331df91
commit 3b380b17d2
1 changed files with 15 additions and 5 deletions
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20
sudoku/solvers/backtracker.py
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@ -12,21 +12,21 @@ def solve(sudoku):
return _solve_square(sudoku, 0, 0) return _solve_square(sudoku, 0, 0)
def _solve_square(sudoku, x, y): def _solve_square(sudoku, x, y):
should_backtrack = False
for value in sudoku.possible_values: for value in sudoku.possible_values:
should_backtrack = False
try: try:
print('({},{}) trying {}'.format(x, y, value))
sudoku.set(x, y, value) sudoku.set(x, y, value)
except SquareIsClue: except SquareIsClue:
# Do nothing with this square; continue on to the next square below. # Do nothing with this square; continue on to the next square below.
print('({},{}) square is clue'.format(x,y))
pass pass
except ValueExistsInPeers: except ValueExistsInPeers:
print('({},{}) value exists in peer set'.format(x,y))
# Try next value. # Try next value.
should_backtrack = True
continue continue
except NoPossibleValues: except NoPossibleValues:
# Need to backtrack. # Need to backtrack.
print('({},{}) backtracking'.format(x,y)) sudoku.unset(x, y)
raise Backtrack() raise Backtrack()
next_coord = _next_coord(sudoku, x, y) next_coord = _next_coord(sudoku, x, y)
@ -34,9 +34,19 @@ def _solve_square(sudoku, x, y):
break break
try: try:
_solve_square(sudoku, *next_coord) return _solve_square(sudoku, *next_coord)
except Backtrack: except Backtrack:
should_backtrack = True
continue continue
if should_backtrack:
# Unhandled backtrack. Pop out of this one too.
try:
sudoku.unset(x, y)
except SquareIsClue:
pass
raise Backtrack()
return sudoku return sudoku
def _next_coord(sudoku, x, y): def _next_coord(sudoku, x, y):