function solve(n) {
  var ans = []
  solver([])
  return ans
  function solver(current) {
    if (current.length === n)
      ans.push(current)
    else
      for (var i=0; i < n; i++) {
        for (var j=0, l=current.length; j < l; j++) {
          var prev = current[j]
          if (prev === i)
            break
          if (prev-(l-j) === i)
            break
          if (prev+(l-j) === i)
            break
        }
        if (j === l)
          solver(current.concat([i]))
      }
  }
}