8. Custom constraints: the alldifferent_except_0 constraint

The global alldifferent_except_0 constraint is exactly as its name says: an alldifferent constraint except for the variables that have a 0 value. Although this constraint is already implemented in or-tools[1], we will spend the whole chapter dissecting this constraint and learn how to implement our own customized version.

Classes under scrutiny:

Files:

You can find the code in the directory documentation/tutorials/cplusplus/chap4.

The files inside this directory are:

Content:

• 8.1. The alldifferent_except_0 constraint
  • 8.1.1. Definition
  • 8.1.2. The implemented AllDifferentExcept
  • 8.1.3. Use
  • 8.1.4. A first example: The Partial Latin Square Extension Problem (PLSE)
• 8.2. Basic working of the solver: constraints
  • 8.2.1. BaseObject
  • 8.2.2. Demons
  • 8.2.3. The BaseObject and PropagationBaseObject classes
  • 8.2.4. The propagation queue
  • 8.2.5. The Constraint class
  • 8.2.6. Propagation in action: the PropagationMonitor class
• 8.3. Consistency in a nutshell
• 8.4. A basic Constraint example: the XXX Constraint
  • 8.4.1. The AllDifferentExcept constraint more in details
• 8.5. First approach: model the constraint
  • 8.5.1. First model
• 8.6. The AllDifferent constraint in more details
• 8.7. Second approach: a custom Constraint
  • 8.7.1. Well
• 8.8. Summary

Footnote

[1]	The implemented constraint is a little bit more general and doesn’t consider 0 as a special value. We’ll discuss this constraint in the section The alldifferent_except_0 constraint.