Algorithm to convert string to int while mainting lexicographical order

Question

I need an algorithm that will map a string of length four to a four digit number. The problem is it has to maintain lexicographical order. It doesn't need to not have collisions, it's just that if S <= T, F(S) <= F(T). The only additional constraint is that it should be surjective: all numbers must be mapped to by some string.

Surely F(S) = 9999 is not what you're looking for, yet it satisfies the constraints. — David Eisenstat, Oct 16 '14 at 19:48
@DavidEisenstat Good catch. The other constraint was that it's surjective: all numbers can be produced. — Alex Beals, Oct 16 '14 at 21:12
Ah. What exactly is the domain of F, then? (e.g., strings of length exactly four, comprised entirely of characters in the class `[A-Za-z]`) — David Eisenstat, Oct 16 '14 at 21:16
Assuming characters are integers between MIN and MAX inclusively: `y[i]=(x[i]-MIN)*10/(MAX-MIN+1)` (not tested) — n. m. could be an AI, Oct 16 '14 at 21:43

score 1 · Accepted Answer · answered Oct 16 '14 at 21:43

1

Can't you just map letters to digits directly, grouping a few at a time to handle the fact that there are more letters than digits? {a, b, c} => 1, {d, e, f} => 2 etc.

answered Oct 16 '14 at 21:43

MattPutnam

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Algorithm to convert string to int while mainting lexicographical order

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