/// <summary>
/// Eliminate will remove the value from the tile and propagate changes via calls to Assign
/// if there is only a single value remaining
/// NOTE: This method mutates the CPBoard cpb parameter
/// </summary>
/// <param name="cpb"></param>
/// <param name="tile"></param>
/// <param name="value"></param>
/// <returns></returns>
static public bool Eliminate(CPBoard cpb, int tileIndex, string value)
{
var values = cpb.Get(tileIndex);
CDebug.Assert(values.Length > 0, "values.Length > 0");
if (values.Length == 1)
{
// Reached a contradiction, eliminating this value will leave the tile EMPTY!
if (values == value)
{
return(false);
}
// Value has already been eliminated from this tile
return(true);
}
var newValues = values.Replace(value, "");
cpb.Set(tileIndex, newValues);
// If there is only one possible value after the change
// Call assign to propagate changes
if (newValues.Length == 1)
{
return(Assign(cpb, tileIndex, newValues));
}
return(true);
}
public void TestCopy()
{
var cpb = new CPBoard(bSolvableByCP);
CPBoard copy = cpb.Copy();
// Changing original does not mutate copy
Assert.NotEqual("4", copy.Get(0));
cpb.Set(0, "4");
Assert.NotEqual("4", copy.Get(0));
// Chaning copy does not change original
Assert.NotEqual("2", cpb.Get(1));
copy.Set(1, "2");
Assert.NotEqual("2", cpb.Get(1));
}
/// <summary>
/// Assign a single value to the tile, propagate the changes via calls to Eliminate
/// NOTE: Method mutates the CPBoard cpb parameter
/// </summary>
/// <param name="cpb"></param>
/// <param name="tileIndex"></param>
/// <param name="value"></param>
/// <returns></returns>
static public bool Assign(CPBoard cpb, int tileIndex, string value)
{
CDebug.Assert(value.Length == 1, "Cannot assign multiple values");
var values = cpb.Get(tileIndex);
// Cannot assign a value that is a not possible value of the tile
if (!values.Contains(value))
{
return(false);
}
// Attempt to eliminate values from peers
cpb.Set(tileIndex, value);
foreach (var peer in Peers[tileIndex])
{
if (!Eliminate(cpb, peer, value))
{
return(false);
}
}
return(true);
}
