{
  "name": "langford_n11__v4_nh",
  "problem_type": "langford",
  "params": {
    "n": 11
  },
  "prompt": "Construct a Langford sequence L(2,11): a sequence of length 22 containing exactly 2 copies of each integer from 1 to 11, such that the two occurrences of each value v are exactly v+1 positions apart (so copies of 1 are 1 position apart, copies of 2 are 2 positions apart, etc.). Example: L(2,3) has solution [2, 3, 1, 2, 1, 3].\n\nReturn seq as a list of 22 integers in 1..11, or state \"UNSATISFIABLE\" if no such sequence exists.",
  "satisfiable": true,
  "solution": {
    "seq": [
      6,
      2,
      3,
      11,
      2,
      10,
      3,
      6,
      9,
      1,
      8,
      1,
      4,
      7,
      5,
      11,
      10,
      4,
      9,
      8,
      5,
      7
    ]
  },
  "difficulty": {
    "solve_time_ms": 1587.0,
    "search_space": 1124000727777607680000,
    "num_variables": 22,
    "num_constraints": 258,
    "num_edges": -1,
    "backend": "pycsp",
    "solve_tier": "hard",
    "solve_pct_global": 87.78,
    "solve_pct_type": 31.25
  },
  "partial_assignment": null
}