Miscellaneous cleanup.

[pseudoku.git] / pseudoku / grid / constraints.py

diff --git a/pseudoku/grid/constraints.py b/pseudoku/grid/constraints.py
index 2495102..e1ea667 100644 (file)
--- a/pseudoku/grid/constraints.py
+++ b/pseudoku/grid/constraints.py
@@ -7,6 +7,11 @@ class Constraint(object):
 
     ### Accessors
 
+    # True iff a constraint consists of a straight line of cells.  Used to
+    # quickly skip over pairs of constraints that cannot possibly have more
+    # than one cell in common.
+    is_linear = False
+
     # NOTE: _cells is a list of refs; _grid is a ref
     # XXX document this
     cells = property(lambda self: [ x() for x in self._cells ])
@@ -28,6 +33,14 @@ class Constraint(object):
         return possible_cells
 
     def resolve_uniques(self):
+        """Searches for values that can only appear in one cell, and sets them
+        appropriately.
+
+        Returns the number of cell changes.
+        """
+
+        cell_changes = 0
+
         for value in xrange(self.grid.size):
             # XXX cache values that are taken care of
             possible_cells = self.find_value(value)
@@ -43,7 +56,9 @@ class Constraint(object):
                 continue
 
             # Only cell in the group that can be value
-            target_cell.set(value)
+            cell_changes += target_cell.set(value)
+
+        return cell_changes
 
 
 class Box(Constraint):
@@ -68,6 +83,8 @@ class Box(Constraint):
 
 
 class Row(Constraint):
+    is_linear = True
+
     def __init__(self, grid, position):
         self._grid = ref(grid)
         self._pos = position
@@ -77,6 +94,8 @@ class Row(Constraint):
             self._cells.append(ref(self.grid.cell(self._pos, col)))
 
 class Column(Constraint):
+    is_linear = True
+
     def __init__(self, grid, position):
         self._grid = ref(grid)
         self._pos = position
@@ -86,6 +105,8 @@ class Column(Constraint):
             self._cells.append(ref(self.grid.cell(row, self._pos)))
 
 class Diagonal(Constraint):
+    is_linear = True
+
     def __init__(self, grid, direction='down', offset=0):
         self._grid = ref(grid)
         self._direction = direction