old    updated
      a               count   count           aux
 0   412           0    0       01         0   410
 1   012           1    1       123        1   101
 2   101           2    2       34567      2   201
 3   432           3    4       7         3   412
 4   302           4    0       7         4   012
 5   201           5    0       7         5   432
 6   410           6    0       7         6   302
                   .    .       .
                   .    .       .
                   9    0       7
   

For the last step, copy aux back into a.