private GridState MoveToNewState(
GridState state,
int xDelta,
int yDelta,
int keysBitmask)
{
int newX = state.Location.X + xDelta;
int newY = state.Location.Y + yDelta;
var p = new Point(newX, newY);
if (!grid.ContainsKey(p))
{
return(null);
}
char c = grid[p];
if (c == '#')
{
// hit a wall
return(null);
}
if (c >= 'A' && c <= 'Z')
{
// this is a door
// key for this door is the associated lowercase letter
char key = (char)(c + 32);
int keybit = CharToBit(key);
// if the key for this door is not in all the keys
if ((keysBitmask & keybit) == 0)
{
// this key is not in the keys we are looking for
// at all, so for part 2 it's in a different
// quadrant of the grid
return(new GridState
{
Location = new Point(newX, newY),
OriginalLocation = state,
BitMask = state.BitMask,
Steps = state.Steps + 1
});
}
// if the key is in the state's found keys - found the key
// for this door already so we can move there
if ((state.BitMask & keybit) != 0)
{
return(new GridState
{
Location = new Point(newX, newY),
BitMask = state.BitMask,
OriginalLocation = state,
Steps = state.Steps + 1
});
}
// can't go here
return(null);
}
if (c >= 'a' && c <= 'z')
{
// we are at another key, pick it up
// and move to this location
return(new GridState
{
Location = new Point(newX, newY),
Steps = state.Steps + 1,
OriginalLocation = state,
BitMask = state.BitMask | CharToBit(c)
});
}
// otherwise this is an empty location,
// move there but don't update keys or anything
return(new GridState
{
Location = new Point(newX, newY),
BitMask = state.BitMask,
OriginalLocation = state,
Steps = state.Steps + 1
});
}
