## Class NearestCityPairHeuristic

• All Implemented Interfaces:
`ConstructiveHeuristic<Permutation>`

```public final class NearestCityPairHeuristic
extends Object
implements ConstructiveHeuristic<Permutation>```
This class implements a constructive heuristic for the TSP that prefers the first city of the nearest pair of cities. Since the stochastic sampling algorithms of the library require higher heuristic values to imply preferred choice, this heuristic is implemented as: h(i) == 1.0 / (1.0 + distance(j, i) + mink(distance(i, k))), where h(i) is the heuristic value for city i, and j is the most recently added city.
• ### Constructor Summary

Constructors
Constructor Description
`NearestCityPairHeuristic​(TSP problem)`
Constructs a nearest city pair heuristic for an instance of the TSP.
• ### Method Summary

All Methods
Modifier and Type Method Description
`int` `completeLength()`
Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured.
`IncrementalEvaluation<Permutation>` `createIncrementalEvaluation()`
Creates an IncrementalEvaluation object corresponding to an initially empty Partial for use in incrementally constructing a solution to the problem for which this heuristic is designed.
`Partial<Permutation>` `createPartial​(int n)`
Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length.
`Problem<Permutation>` `getProblem()`
Gets a reference to the instance of the optimization problem that is the subject of this heuristic.
`double` ```h​(Partial<Permutation> p, int element, IncrementalEvaluation<Permutation> incEval)```
Heuristically evaluates the possible addition of an element to the end of a Partial.
• ### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
• ### Constructor Detail

• #### NearestCityPairHeuristic

`public NearestCityPairHeuristic​(TSP problem)`
Constructs a nearest city pair heuristic for an instance of the TSP.
Parameters:
`problem` - The TSP instance to solve.
• ### Method Detail

• #### h

```public double h​(Partial<Permutation> p,
int element,
IncrementalEvaluation<Permutation> incEval)```
Description copied from interface: `ConstructiveHeuristic`
Heuristically evaluates the possible addition of an element to the end of a Partial. Higher evaluations imply that the element is a better choice for the next element to add. For example, if you evaluate two elements, x and y, with h, and h returns a higher value for y than for x, then this means that y is believed to be the better choice according to the heuristic. Implementations of this interface must ensure that h always returns a positive result. This is because stochastic sampling algorithms such as HBSS and VBSS assume that the constructive heuristic returns only positive values.
Specified by:
`h` in interface `ConstructiveHeuristic<Permutation>`
Parameters:
`p` - The current state of the Partial
`element` - The element under consideration for adding to the Partial
`incEval` - An IncrementalEvaluation of p. This method assumes that incEval is of the same runtime type as the object returned by `ConstructiveHeuristic.createIncrementalEvaluation()`.
Returns:
The heuristic evaluation of the hypothetical addition of element to the end of p. The higher the evaluation, the more important the heuristic believes that element should be added next. The intention is to compare the value returned with the heuristic evaluations of other elements. Individual results in isolation are not necessarily meaningful.
• #### getProblem

`public final Problem<Permutation> getProblem()`
Description copied from interface: `ConstructiveHeuristic`
Gets a reference to the instance of the optimization problem that is the subject of this heuristic.
Specified by:
`getProblem` in interface `ConstructiveHeuristic<Permutation>`
Returns:
the instance of the optimization problem that is the subject of this heuristic.
• #### createPartial

`public final Partial<Permutation> createPartial​(int n)`
Description copied from interface: `ConstructiveHeuristic`
Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length.
Specified by:
`createPartial` in interface `ConstructiveHeuristic<Permutation>`
Parameters:
`n` - the desired length of the final complete solution.
Returns:
an empty Partial solution
• #### completeLength

`public final int completeLength()`
Description copied from interface: `ConstructiveHeuristic`
Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured.
Specified by:
`completeLength` in interface `ConstructiveHeuristic<Permutation>`
Returns:
length of solutions to the problem instance for which this heuristic is configured