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magic_sequence_sat

<table align="left"> <td> <a href="https://colab.research.google.com/github/google/or-tools/blob/main/examples/notebook/contrib/magic_sequence_sat.ipynb">Run in Google Colab</a> </td> <td> <a href="https://github.com/google/or-tools/blob/main/examples/contrib/magic_sequence_sat.py">View source on GitHub</a> </td> </table>

First, you must install ortools package in this colab.

python

%pip install ortools

Solve the magic sequence problem with the CP-SAT solver.

python

from ortools.sat.python import cp_model


def main():
  """Magic sequence problem."""
  n = 100
  values = range(n)

  model = cp_model.CpModel()

  x = [model.NewIntVar(0, n, 'x%i' % i) for i in values]

  for k in values:
    tmp_array = []
    for i in values:
      tmp_var = model.NewBoolVar('')
      model.Add(x[i] == k).OnlyEnforceIf(tmp_var)
      model.Add(x[i] != k).OnlyEnforceIf(tmp_var.Not())
      tmp_array.append(tmp_var)
    model.Add(sum(tmp_array) == x[k])

  # Redundant constraint.
  model.Add(sum(x) == n)

  solver = cp_model.CpSolver()
  # No solution printer, this problem has only 1 solution.
  solver.parameters.log_search_progress = True
  solver.Solve(model)
  print(solver.ResponseStats())
  for k in values:
    print('x[%i] = %i ' % (k, solver.Value(x[k])), end='')
  print()


main()