Solver

```
public interface Solver
```
The interface Solver is used for Problem Resolution and utilizes concepts of Search Strategies and Solutions.
The Solver provides a standardized way to implement the following functions:
- Find a solution
- Find an optimal solution that minimizes/maximizes an objective variable
- Iterate through multiple solutions
- Limit search time and a number of solutions.
These functions use an ordered list of search strategies called "execution list". Each implementation should provide at least one default search strategy that is available by the Solver's method "getSearchStrategy". A user may get this strategy and apply its methods "setVars", "setVarSelector", and "setValueSelector" to customize it. This strategy is the first one to be executed. A user may also add another strategy using the Solver's method "newSearchStrategy". It returns a new instance of the default search strategy. A user may set its attributes and use the method "addStrategy" to add a new customized strategy to the end of the execution list. For example, if a user want first to instantiate all variables from the array "types" and then all variables from the array "counts", it can be done as follow:
```
 SearchStrategy s1 = solver.getSearchStrategy();
 s1.setVars(types);
 SearchStrategy s2 = solver.newSearchStrategy();
 s2.setVars(counts);
 s2.setVarSelectorType(VarSelectorType.RANDOM);
 solver.addStrategy(s2);
 
```
See Also:

Solution, SearchStrategy, VarSelector, ValueSelector

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`void`	`addSearchStrategy(SearchStrategy strategy)` This methods adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars)` This methods takes the default search strategy, resets its vars, and adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, ValueSelector valueSelector)` This methods takes the default search strategy, resets its vars and valueSelector, and adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, ValueSelectorType valueSelectorType)` This methods takes the default search strategy, resets its vars and valueSelector, and adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, VarSelector varSelector)` This methods takes the default search strategy, resets its vars and varSelector, and adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, VarSelectorType varSelectorType)` This methods takes the default search strategy, resets its vars and varSelector, and adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, VarSelectorType varSelectorType, ValueSelectorType valueSelectorType)` This methods takes the default search strategy, resets its vars, varSelector, and valueSelector, and then adds this strategy to the end of the strategy execution lists.
`void`	`addSearchStrategy(Var[] vars, VarSelector varSelector, ValueSelector valueSelector)` This methods takes the default search strategy, resets its vars, varSelector, and valueSelector, and then adds this strategy to the end of the strategy execution lists.
`void`	`addStrategyLogVariables()` This methods adds the strategy getStrategyLogVariables() to the end of the strategy execution lists.
`Solution[]`	`findAllSolutions()` This method attempts to find all solutions for the Problem.
`Solution`	`findOptimalSolution(Objective objective, Var objectiveVar)` This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar,OptimizationStrategy.NATIVE) It is usually overridden by an implementation
`Solution`	`findOptimalSolution(Objective objective, Var objectiveVar, OptimizationStrategy optStrategy)` This method attempts to find the solution that minimizes/maximizes the objective variable.
`Solution`	`findOptimalSolution(Objective objective, VarReal objectiveVar)` This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar,OptimizationStrategy.NATIVE) It is usually overridden by an implementation
`Solution`	`findOptimalSolution(Objective objective, VarReal objectiveVar, OptimizationStrategy optStrategy)`
`Solution`	`findOptimalSolution(Var objectiveVar)` This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar)
`Solution`	`findOptimalSolution(VarReal objectiveVar)` This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar)
`Solution`	`findSolution()` This method is equivalent to findSolution(DO_NOT_RESTORE); It means that the problem state will always be restored even when a solution is found.
`Solution`	`findSolution(ProblemState restoreOrNot)` This method attempts to find a solution of the problem, for which the solver was defined.
`int`	`getMaxNumberOfSolutions()` Returns the maximal number of solutions any search can look for.
`int`	`getNumberOfSolutions()` Returns the number of the last solution found, or 0 if no solutions have been found yet (or the search for a solution was not yet launched).
`int`	`getOptimizationTolerance()` Returns the current tolerance for the method findOptimalSolution()
`Problem`	`getProblem()` Returns the Problem for which this solver was created
`SearchStrategy`	`getSearchStrategy()` Returns a SearchStrategy that is currently used by the solver
`Solution`	`getSolution(int i)` Returns the i-th Solution found by the latest search
`SearchStrategy`	`getStrategyLogVariables()` Returns a search strategy that logs all variables
`int`	`getTimeLimit()` Returns the duration, in milliseconds, of the imposed time limit on search of one solution.
`int`	`getTimeLimitGlobal()` Returns the duration, in milliseconds, of the imposed time limit on global search of all solutions or an optimal solution.
`long`	`getTimeLimitStart()` Returns the time, in milliseconds, at which the time limit began counting.
`void`	`logStats()` This method logs execution statistics such as a number of choice points, number of failures, used memory, etc.
`SearchStrategy`	`newSearchStrategy()` This methods returns a new default search strategy
`void`	`restoreProblem()` Restores a previously saved problem
`void`	`saveProblem()` Creates a copy of the problem in its current state
`void`	`setMaxNumberOfSolutions(int maxNumberOfSolutions)` Sets the limit on the maximal number of solutions any search can look for.
`void`	`setOptimizationTolerance(int tolerance)` Specifies a tolerance for the method findOptimalSolution().
`void`	`setProblem(Problem problem)` Set the Problem with which this solver should work
`void`	`setSearchStrategy(SearchStrategy strategy)` Define a search strategy that will be used by the solver to solve the problem.
`void`	`setSearchStrategy(Var[] vars)` Define a searchStrategy that will be used by find solutions methods.
`void`	`setSearchStrategy(Var[] vars, ValueSelector valueSelector)` Define a searchStrategy that will be used by find solutions methods.
`void`	`setSearchStrategy(Var[] vars, VarSelector varSelector)` Define a searchStrategy that will be used by find solutions methods.
`void`	`setSearchStrategy(Var[] vars, VarSelector varSelector, ValueSelector valueSelector)` Define a searchStrategy that will be used by find solutions methods.
`void`	`setTimeLimit(int mills)` Sets the duration, in milliseconds, of the time limit on search of one solution.
`void`	`setTimeLimitGlobal(int mills)` Sets the duration, in milliseconds, of the time limit on global search of all solutions or an optimal solution.
`void`	`setTimeLimitStart()` Sets the start time as the system current time, for counting milliseconds to the time limit.
`SolutionIterator`	`solutionIterator()` Creates a solution iterator that allows a user to find and navigate through solutions using the default search strategy.
`void`	`trace(Var var)` This method forces to trace (to log) all modification events for the variable "var".
`void`	`trace(Var[] vars)` This method forces to trace (to log) all modification events for all variables "vars"
`void`	`trace(VarSet setVar)` This method forces to trace (to log) all modification events for the variable "setVar".
`void`	`traceExecution(boolean trueOrFalse)` This method forces the execution to log important execution points
`void`	`traceFailures(boolean flag)` If flag is true, all failures will be traced (logged)
`void`	`traceSolutions(boolean trueOrFalse)` This method forces the execution to log intermediate solutions during optimization search

- Method Detail
  - addSearchStrategy
```
void addSearchStrategy(SearchStrategy strategy)
```
    This methods adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    strategy -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars)
```
    This methods takes the default search strategy, resets its vars, and adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       ValueSelector valueSelector)
```
    This methods takes the default search strategy, resets its vars and valueSelector, and adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    valueSelector -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       ValueSelectorType valueSelectorType)
```
    This methods takes the default search strategy, resets its vars and valueSelector, and adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    valueSelectorType -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       VarSelector varSelector)
```
    This methods takes the default search strategy, resets its vars and varSelector, and adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    varSelector -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       VarSelectorType varSelectorType)
```
    This methods takes the default search strategy, resets its vars and varSelector, and adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    varSelectorType -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       VarSelectorType varSelectorType,
                       ValueSelectorType valueSelectorType)
```
    This methods takes the default search strategy, resets its vars, varSelector, and valueSelector, and then adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    varSelectorType -
    
    valueSelectorType -
  - addSearchStrategy
```
void addSearchStrategy(Var[] vars,
                       VarSelector varSelector,
                       ValueSelector valueSelector)
```
    This methods takes the default search strategy, resets its vars, varSelector, and valueSelector, and then adds this strategy to the end of the strategy execution lists.
    
    Parameters:
    
    vars -
    
    varSelector -
    
    valueSelector -
  - addStrategyLogVariables
```
void addStrategyLogVariables()
```
    This methods adds the strategy getStrategyLogVariables() to the end of the strategy execution lists.
  - findAllSolutions
```
Solution[] findAllSolutions()
```
    This method attempts to find all solutions for the Problem. It uses the default search strategy or the strategy defined by the latest method setSearchStrategy(). It returns an array of found solutions or null if there are no solutions. A user has to be careful not to overload the available memory because the number of found solutions could be huge. The process of finding all solutions can be also controlled by:
    - MaxNumberOfSolutions that is the total number of considered solutions that may be limited by the method setMaxNumberOfSolutions();
    - TotalTimeLimit that is the number of seconds allocated for the entire optimization process.
    The problem state after the execution of this method is always restored.
    Returns:
    
    Solution[]
  - findOptimalSolution
```
Solution findOptimalSolution(Objective objective,
                             Var objectiveVar)
```
    This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar,OptimizationStrategy.NATIVE) It is usually overridden by an implementation
    
    Parameters:
    
    objectiveVar -
    
    Returns:
    
    Solution if a solution is found, null if there are no solutions.
  - findOptimalSolution
```
Solution findOptimalSolution(Objective objective,
                             Var objectiveVar,
                             OptimizationStrategy optStrategy)
```
    This method attempts to find the solution that minimizes/maximizes the objective variable. It uses the search strategy defined by the method setSearchStrategy(strategy). The optimization process can be also controlled by:
    - OptimizationTolerance that is a difference between optimal solutions - see setOptimizationTolarance()
    - MaxNumberOfSolutions that is the total number of considered solutions - may be limited by the method setMaxNumberOfSolutions()
    - TimeLimitGlobal that is the number of seconds allocated for the entire optimization process.
    At the same time the time for one iteration inside optimization loop (a search of one solution) can be also limited by the Solver's attribute TimeLimit or by the use of a special search strategy specified by a particular implementation.
    The problem state after the execution of this method is always restored. All variables that were added to the problems (plus the objectiveVar) will have their assigned values saved inside the optimal solution.
    Parameters:
    
    objective - Objective.MINIMIZE or Objective.MAXIMIZE
    
    objectiveVar - the variable that is being minimized/maximized
    
    optStrategy - OptimizationStrategy (BASIC, DICHOTOMIZE, or NATIVE)
    
    Returns:
    
    Solution if a solution is found, null if there are no solutions.
  - findOptimalSolution
```
Solution findOptimalSolution(Objective objective,
                             VarReal objectiveVar)
```
    This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar,OptimizationStrategy.NATIVE) It is usually overridden by an implementation
    
    Parameters:
    
    objectiveVar -
    
    Returns:
    
    Solution if a solution is found, null if there are no solutions.
  - findOptimalSolution
```
Solution findOptimalSolution(Objective objective,
                             VarReal objectiveVar,
                             OptimizationStrategy optStrategy)
```
  - findOptimalSolution
```
Solution findOptimalSolution(Var objectiveVar)
```
    This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar)
    
    Parameters:
    
    objectiveVar -
    
    Returns:
    
    Solution if a solution is found, null if there are no solutions.
  - findOptimalSolution
```
Solution findOptimalSolution(VarReal objectiveVar)
```
    This method is equivalent to findOptimalSolution(Objective.MINIMIZE,objectiveVar)
    
    Parameters:
    
    objectiveVar -
    
    Returns:
    
    Solution if a solution is found, null if there are no solutions.
  - findSolution
```
Solution findSolution()
```
    This method is equivalent to findSolution(DO_NOT_RESTORE); It means that the problem state will always be restored even when a solution is found.
    
    Returns:
    
    a Solution if the search is successful or null.
  - findSolution
```
Solution findSolution(ProblemState restoreOrNot)
```
    This method attempts to find a solution of the problem, for which the solver was defined. It uses the search strategy defined by the method setSearchStrategy(). It returns the found solution (if any) or null. It also saves the solution and makes it available through the method getSolution(). If a solution is not found, the problem state is restored to that of before the invocation of this method. If a solution is found, the problem state will be restored only if the parameter "restore" is true. Otherwise all problem variables will be instantiated with the solution values. The search can be limited by time, number of failed attempts, etc.
    
    Parameters:
    
    restoreOrNot - defines if the problem state should be restored after a solution is found
    
    Returns:
    
    a Solution if the search is successful or null
  - getMaxNumberOfSolutions
```
int getMaxNumberOfSolutions()
```
    Returns the maximal number of solutions any search can look for. A value of -1 indicates infinity, i.e. that there is no limitation on the maximal number of solutions. The default value is -1.
    
    Returns:
    
    the maximal number of solutions any search can look for. A value of -1 indicates infinity, i.e. that there is no limitation on the maximal number of solutions. The default value is -1.
  - getNumberOfSolutions
```
int getNumberOfSolutions()
```
    Returns the number of the last solution found, or 0 if no solutions have been found yet (or the search for a solution was not yet launched).
    
    Returns:
    
    the number of the last solution found, or 0 if no solution have been found yet (or the search for a solution was not yet launched).
  - getOptimizationTolerance
```
int getOptimizationTolerance()
```
    Returns the current tolerance for the method findOptimalSolution()
    
    Returns:
    
    the current tolerance for the method findOptimalSolution()
  - getProblem
```
Problem getProblem()
```
    Returns the Problem for which this solver was created
    
    Returns:
    
    the Problem for which this solver was created
  - getSearchStrategy
```
SearchStrategy getSearchStrategy()
```
    Returns a SearchStrategy that is currently used by the solver
    
    Returns:
    
    a SearchStrategy that is currently used by the solver to solve the problem
  - getSolution
```
Solution getSolution(int i)
```
    Returns the i-th Solution found by the latest search
    
    Returns:
    
    the i-th Solution found by the latest search
    
    See Also:
    
    findAllSolutions()
  - getStrategyLogVariables
```
SearchStrategy getStrategyLogVariables()
```
    Returns a search strategy that logs all variables
    
    Returns:
    
    a a search strategy that logs all variables
  - getTimeLimit
```
int getTimeLimit()
```
    Returns the duration, in milliseconds, of the imposed time limit on search of one solution.
    
    Returns:
    
    the duration, in milliseconds, of the imposed time limit on search of one solution.
  - getTimeLimitGlobal
```
int getTimeLimitGlobal()
```
    Returns the duration, in milliseconds, of the imposed time limit on global search of all solutions or an optimal solution.
    
    Returns:
    
    the duration, in milliseconds, of the imposed time limit on global search of all solutions or an optimal solution.
  - getTimeLimitStart
```
long getTimeLimitStart()
```
    Returns the time, in milliseconds, at which the time limit began counting.
    
    Returns:
    
    the time, in milliseconds, at which the time limit began counting.
  - logStats
```
void logStats()
```
    This method logs execution statistics such as a number of choice points, number of failures, used memory, etc. This method is expected to be specific for different reference implementations
  - newSearchStrategy
```
SearchStrategy newSearchStrategy()
```
    This methods returns a new default search strategy
    
    Returns:
    
    a new default search strategy
  - restoreProblem
```
void restoreProblem()
```
    Restores a previously saved problem
  - saveProblem
```
void saveProblem()
```
    Creates a copy of the problem in its current state
  - setMaxNumberOfSolutions
```
void setMaxNumberOfSolutions(int maxNumberOfSolutions)
```
    Sets the limit on the maximal number of solutions any search can look for. A value of -1 indicates infinity, i.e. that there is no limitation on the maximal number of solutions. The default value is -1.
    
    Parameters:
    
    maxNumberOfSolutions - the new limit for the maximal number of solutions any search can look for.
  - setOptimizationTolerance
```
void setOptimizationTolerance(int tolerance)
```
    Specifies a tolerance for the method findOptimalSolution(). If the difference between newly found solution and a previous one is less or equal "tolerance" then the last solution is considered to be the optimal one. By default, the optimization tolerance is 0.
    
    Parameters:
    
    tolerance -
  - setProblem
```
void setProblem(Problem problem)
```
    Set the Problem with which this solver should work
  - setSearchStrategy
```
void setSearchStrategy(SearchStrategy strategy)
```
    Define a search strategy that will be used by the solver to solve the problem. Each Solver' implementation should set a default search strategy in the its Solver constructor.
    
    Parameters:
    
    strategy -
  - setSearchStrategy
```
void setSearchStrategy(Var[] vars)
```
    Define a searchStrategy that will be used by find solutions methods. This methods takes the default search strategy, and resets its vars.
    
    Parameters:
    
    vars -
  - setSearchStrategy
```
void setSearchStrategy(Var[] vars,
                       ValueSelector valueSelector)
```
    Define a searchStrategy that will be used by find solutions methods. This methods takes the default search strategy, and resets its vars and valueSelector.
    
    Parameters:
    
    vars -
    
    valueSelector -
  - setSearchStrategy
```
void setSearchStrategy(Var[] vars,
                       VarSelector varSelector)
```
    Define a searchStrategy that will be used by find solutions methods. This methods takes the default search strategy, and resets its vars and varSelector.
    
    Parameters:
    
    vars -
    
    varSelector -
  - setSearchStrategy
```
void setSearchStrategy(Var[] vars,
                       VarSelector varSelector,
                       ValueSelector valueSelector)
```
    Define a searchStrategy that will be used by find solutions methods. This methods takes the default search strategy, and resets its vars, varSelector, and valueSelector.
    
    Parameters:
    
    vars -
    
    varSelector -
    
    valueSelector -
  - setTimeLimit
```
void setTimeLimit(int mills)
```
    Sets the duration, in milliseconds, of the time limit on search of one solution.
    
    Parameters:
    
    mills - the new time limit in milliseconds
  - setTimeLimitGlobal
```
void setTimeLimitGlobal(int mills)
```
    Sets the duration, in milliseconds, of the time limit on global search of all solutions or an optimal solution.
    
    Parameters:
    
    mills - the new global time limit in milliseconds
  - setTimeLimitStart
```
void setTimeLimitStart()
```
    Sets the start time as the system current time, for counting milliseconds to the time limit.
  - solutionIterator
```
SolutionIterator solutionIterator()
```
    Creates a solution iterator that allows a user to find and navigate through solutions using the default search strategy.
    
    Returns:
    
    a solution iterator
  - trace
```
void trace(Var var)
```
    This method forces to trace (to log) all modification events for the variable "var".
    
    Parameters:
    
    var -
  - trace
```
void trace(Var[] vars)
```
    This method forces to trace (to log) all modification events for all variables "vars"
    
    Parameters:
    
    vars -
  - trace
```
void trace(VarSet setVar)
```
    This method forces to trace (to log) all modification events for the variable "setVar".
    
    Parameters:
    
    setVar -
  - traceExecution
```
void traceExecution(boolean trueOrFalse)
```
    This method forces the execution to log important execution points
    
    Parameters:
    
    trueOrFalse - boolean
  - traceFailures
```
void traceFailures(boolean flag)
```
    If flag is true, all failures will be traced (logged)
    
    Parameters:
    
    flag -
  - traceSolutions
```
void traceSolutions(boolean trueOrFalse)
```
    This method forces the execution to log intermediate solutions during optimization search
    
    Parameters:
    
    trueOrFalse - boolean

Interface Solver

Method Summary

Method Detail

addSearchStrategy

addSearchStrategy

addSearchStrategy

addSearchStrategy

addSearchStrategy

addSearchStrategy

addSearchStrategy

addSearchStrategy

addStrategyLogVariables

findAllSolutions

findOptimalSolution

findOptimalSolution

findOptimalSolution

findOptimalSolution

findOptimalSolution

findOptimalSolution

findSolution

findSolution

getMaxNumberOfSolutions

getNumberOfSolutions

getOptimizationTolerance

getProblem

getSearchStrategy

getSolution

getStrategyLogVariables

getTimeLimit

getTimeLimitGlobal

getTimeLimitStart

logStats

newSearchStrategy

restoreProblem

saveProblem

setMaxNumberOfSolutions

setOptimizationTolerance

setProblem

setSearchStrategy

setSearchStrategy

setSearchStrategy

setSearchStrategy

setSearchStrategy

setTimeLimit

setTimeLimitGlobal

setTimeLimitStart

solutionIterator

trace

trace

trace

traceExecution

traceFailures

traceSolutions