Picat Constraint Programming with CP Questions and Answers

Question 1

When modeling a constraint satisfaction problem in Picat using the `cp` module, what is the primary purpose of the `solve/1` predicate?

Accepted Answer

To initiate the search process for finding a valid assignment of values to the variables.

Answer

To declare the domains of the constraint variables.

Answer

To post the arithmetic and global constraints to the solver.

Answer

To verify if a manually assigned set of values satisfies all constraints.

Question 2

A developer is solving a crypto-arithmetic puzzle like `SEND + MORE = MONEY` in Picat. Which global constraint from the `cp` module is essential to ensure that each letter is assigned a unique digit?

Accepted Answer

`alldifferent/1`

Answer

`element/3`

Answer

`sum/1`

Answer

`global_cardinality/2`

Question 3

Which of the following lines of code correctly declares a list of three Picat variables `X`, `Y`, and `Z` as constraint variables, each with a domain of integers from 1 to 10, for use with the `cp` module?

Accepted Answer

`[X, Y, Z] :: 1..10`

Answer

`[X, Y, Z] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}`

Answer

`domain([X, Y, Z], 1, 10)`

Answer

`foreach(V in [X,Y,Z]) V in 1..10 end`

Question 4

What is the fundamental difference between the standard Picat unification operator `=` and the CP constraint equality operator `#=` within a `cp` model?

Accepted Answer

The `=` operator immediately attempts to bind a variable, whereas `#=` posts a constraint that must be satisfied in the final solution.

Answer

The `#=` operator works only with integers, while `=` works with any data type.

Answer

There is no difference; they are interchangeable within a `cp` model.

Answer

The `#=` operator is used for destructive assignment, similar to `:=`, while `=` is for logical unification.

Question 5

A programmer is building a scheduling model where two tasks, Task A and Task B, cannot overlap. Task A starts at time `S1` and has duration `D1`. Task B starts at `S2` and has duration `D2`. Which of the following constraints correctly models that Task A must finish before Task B starts OR Task B must finish before Task A starts?

Accepted Answer

`S1 + D1 #=< S2 #/ S2 + D2 #=< S1`

Answer

`S1 + D1 #!= S2`

Answer

`S1 + D1 #< S2 + D2`

Answer

`alldifferent([S1, D1, S2, D2])`

Question 6

After importing the `cp` module, what is the role of the `indomain/1` predicate?

Accepted Answer

It is a non-deterministic predicate that, upon backtracking, assigns the next value from a variable's domain to that variable.

Answer

It checks if a specific value is within the initial domain of a variable.

Answer

It is a search strategy option used within the `solve/2` predicate.

Answer

It constrains a variable to have a domain that is a subset of another variable's domain.