User:Paolo Liberatore~enwiki/Crypto-arithmetic puzzle

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A crypto-arithmetic puzzle is a puzzle made of an equation over two integer expressions in which numbers are replaced by letters; a solution is an assignment of different digits to the letters in such a way the equation holds. A typical example of a crypto-arithmetic puzzle the "send more money" puzzle, invented by Henry Dudeney and published for the first time in the June 1924 issue of the Strand Magazine. This problem is displayed as follows:

S E N D + M O R E --- M O N E Y

The only solution of this problem is:, as replacing each letter with its corresponding number leads to the following correct equation:

9 5 6 7 + 1 0 8 5 ---  1 0 6 5 2

Another common crypto-arithmetic puzzle is. A French version is  and a German version is. The first of these two puzzles are often used as examples of constraint satisfaction problems or problems that can be solved by constraint programming, often together with the Eight queens puzzle.