Blackjack Bust Calculator
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O%48«⁵µ13R«⁵ẋ4œ-+ṖS$&gt;21S


A monadic link accepting a list of characters (using either the lower-case option OR the upper-case option with 1 for A) which returns the numerator (the number of 49ths) in [0,49].

Try it online! Or see the test-suite

How?

Note that by using lower-case the minimum of 10 and the ordinals modulo by 48 gives the card values. The same holds for upper-case T, J, Q, K and 1 for an ace, as shown on the right (but an upper-case A does not work):

     card:   a   2   3   4   5   6   7   8   9   t   j   q   k   |   1   T   J   Q   K
  ordinal:  97  50  51  52  53  54  55  56  57 116 106 113 107   |  49  84  74  81  75
   mod 48:   1   2   3   4   5   6   7   8   9  20  10  17  11   |   1  36  26  33  27
min(_,10):   1   2   3   4   5   6   7   8   9  10  10  10  10   |   1  10  10  10  10




O%48«⁵µ13R«⁵ẋ4œ-+ṖS$&gt;21S - Link: list of characters   e.g. "q3a"
O                        - ordinals (of the input list)    [113, 51, 97]
 %48                     - modulo by 48                    [17,3,1]
     ⁵                   - ten
    «                    - minimum                         [10,3,1]
      µ                  - start a new monadic chain
       13R               - range of 13                     [1,2,3,4,5,6,7,8,9,10,11,12,13]
           ⁵             - ten                             10
          «              - minimum                         [1,2,3,4,5,6,7,8,9,10,10,10,10]
            ẋ4           - repeat four times               [1,2,3,4,5,6,7,8,9,10,10,10,10,1,2,3,4,5,6,7,8,9,10,10,10,10,1,2,3,4,5,6,7,8,9,10,10,10,10,1,2,3,4,5,6,7,8,9,10,10,10,10]
              œ-         - multi-set difference            [1,2,3,4,5,6,7,8,9,10,10,10,10,1,2,3,4,5,6,7,8,9,10,10,10,10,1,2,3,4,5,6,7,8,9,10,10,10,10  ,2  ,4,5,6,7,8,9   ,10,10,10]
                   $     - last two links as a monad:
                 Ṗ       -   pop                           [10,3]
                  S      -   sum                           13
                +        - add (vectorises)                [14,15,16,17,18,19,20,21,22,23,23,23,23,14,15,16,17,18,19,20,21,22,23,23,23,23,14,15,16,17,18,19,20,21,22,23,23,23,23,15,17,18,19,20,21,22,23,23,23]
                    &gt;21  - greater than 21?                [0,0,0,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,0,0,1,1,1,1,1,0,0,0,0,0,0,1,1,1,1]
                       S - sum                             19