Problem 2318. Combine Cards to make 21

Given between two and six cards, e.g.

 A _ 3 _ 7 _ 6 _ 2

place one of the mathematical symbols (+,-,*,/) in the space between each pair of cards to make the equation equal 21.

The input will be a string, e.g.

• 'A3762'

The output should be a cell array of mathematical symbols in the order that satisfies the puzzle, e.g. for the string given above, the output would be:

{'+-*/'}

Which means that A + 3 - 7 * 6 / 2 = 21.

• A + 3 = 14
• 14 - 7 = 7
• 7 * 6 = 42
• 42 / 2 = 21

Rules:

• The Ace can represent either 1 or 11.
• All operations should be performed from left to right
• Cards will be represented by the characters: A,2,3,4,5,6,7,8,9,J,Q,K