We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once; for example, the 5-digit number, 15234, is 1 through 5 pandigital.
The product 7254 is unusual, as the identity, 39 × 186 = 7254, containing multiplicand, multiplier, and product is 1 through 9 pandigital.
Find the sum of all products whose multiplicand/multiplier/product identity can be written as a 1 through 9 pandigital.
HINT: Some products can be obtained in more than one way so be sure to only include it once in your sum.
This is the first problem that I'll be doing for the first time with the Project Euler 100 Challenge! That is, with all the preceding problems I solved them once ages ago (over a decade), when I first discovered Project Euler. This is the first one I hadn't already solved some other way.
...
Well that was a little fun. A bit of a slowdown from a minor mistake I
made w.r.t. the size of the product (it must be four digit) and some
minor fighting with the compiler over how to ask whether a bool
slice was all true, but it worked.