Returns the locations of all dissatisfied households in the city. A household is dissatisfied if it does not have a sufficient proportion of neighbors that share its demographic. For example, if the city-dwellers desire a similarity of 50%, at least four of a household's eight neighbors need to share its demographic or it will be dissatisfied. (Dissatisfied residents will move when moveResidents is next called.)

When determining a household's neighbors, diagonally adjacent grid locations count, and many households will have a full eight neighbors. However, Vacant locations don’t count as neighbors, nor do locations that are beyond the edges of the grid. A corner location, then, will only have a maximum of three neighbors, less if any of the three locations are vacant.

For example, consider a non-vacant corner location. There are three locations next to it on the grid. If one of them shares the corner’s demographic, another doesn’t, and the third one is vacant (and therefore ignored), then 50% of the corner’s two neighbors are similar to the corner.

Vacant locations are never returned by this method (i.e., they count as satisfied). Any household with zero neighbors is considered to be satisfied.

Advances the most recently launched simulation by one step, moving all dissatisfied households to vacant locations on the grid. During the simulation step, the dissatisfied households move one at a time, in random order, each receiving a random home among the ones that are vacant at that moment. (That is, a household may move to a home vacated by another dissatisfied household earlier during the same simulation step.)

Satisfied residents stay where they are. If a satisfied resident becomes dissatisfied during this simulation step (because others move), that does not cause them to move (yet).

If there are no vacant addresses at all in the city, this method does nothing.

Returns a Map whose keys are all the demographics present in the city (Vacant included) and whose values list all the locations where that demographic is present.

Note to students: This method will only be implemented in Chapter 9.2. You won't need it before that.

Returns the proportion of satisfied residents in the city. For example, a return value of 0.0 means that nobody is satisfied, 1.0 that everyone is, and 0.95 that most are.

Launches a new simulation. The simulation will take place on a newly initialized city grid as specified by the parameters provided. After calling this method, moveResidents will advance the newly launched simulation; any previously ongoing simulation is simply discarded.