Looks like there is a problem with very hard test

clues = [ 0, 2, 3, 0, 2, 0, 0, 
          5, 0, 4, 5, 0, 4, 0,
          0, 4, 2, 0, 0, 0, 6,
          0, 0, 0, 0, 0, 0, 0 ]

expected = [[7, 6, 2, 1, 5, 4, 3],
            [1, 3, 5, 4, 2, 7, 6],
            [6, 5, 4, 7, 3, 2, 1],
            [5, 1, 7, 6, 4, 3, 2],
            [4, 2, 1, 3, 7, 6, 5],
            [3, 7, 6, 2, 1, 5, 4],
            [2, 4, 3, 5, 6, 1, 7]]

My code returns other valid (I believe) solution:

[[7, 6, 1, 2, 5, 4, 3],
 [1, 4, 6, 3, 2, 7, 6],
 [6, 1, 5, 7, 4, 3, 2],
 [5, 7, 4, 6, 3, 2, 1],
 [4, 3, 2, 1, 7, 6, 5],
 [3, 2, 7, 6, 1, 5, 4],
 [2, 5, 3, 4, 6, 1, 7]]

I think there is problem with one test. Namely:

var clues = [ 0, 3, 0, 3, 2, 3,
              3, 2, 0, 3, 1, 0,
              0, 3, 0, 5, 3, 4,
              0, 0, 0, 0, 0, 1];

var expected = [[6,2,3,4,5,1],
                [5,1,6,2,3,4],
                [4,3,5,1,6,2],
                [2,6,4,5,1,3],
                [1,5,2,3,4,6],
                [3,4,1,6,2,5]];

My code returns other valid solution:

[[6,1,5,2,3,4],
 [3,4,6,1,2,5],
 [5,3,4,5,6,1],
 [1,6,3,4,5,2],
 [4,5,2,3,1,6],
 [2,2,1,6,4,3]];

@FrankK, can you please look into this.

I fixed this problem by rounding result values.