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Problem

Your sister and your best friend have been acting rather suspiciously recently. One evening you notice your sister secretly pass a piece of paper into your friend's pocket. You wait for the right opportunity and remove the note to discover the following:

R1U0R0L4L6D5L7D1 L4U6R0R2U4 U6L0D8 R1D1R2.
R1U0L7L4D1U8R2R1 L2L3L8D4D5L2D3!

Confused, you record the secret message and return the piece of paper. The next day, while your sister is out, you look around the house and discover a scrap of paper in one of the waste paper bins. It has the following similar message written on it, but it seems to contain a clue:

R2D1R1L8 = TEST

Can you decode the original message and work out what your sister and best friend are up to?


Solution

The method is, indeed, very misleading and sneaky...

Using the letters D, L, R and U as key markers in the alphabet, the digits that follow represent the numbers of letter after the key marker that the coded letter lies. For example, D3 (3 letters after D) = G.

ABCDEFGHIJKLMNOPQRSTUVWXYZ

Checking with the message on the scrap of paper, R2D1L7L8: R2 (2 letters after R) = T, D1 (1 letter after D) = E, R1 (1 letter after R) = S and L8 (8 letters after L) = T; spelling TEST. Notice how the last letter, T, was disguised by using L rather than R (the nearer marker) to avoid duplication with the first letter, T.

Using this system,

R1U0R0L4L6D5L7D1 L4U6R0R2U4 U6L0D8 R1D1R2.
R1U0L7L4D1U8R2R1 L2L3L8D4D5L2D3!

becomes

SURPRISE PARTY ALL SET.
SUSPECTS NOTHING!

Problem ID: 11 (Aug 2000)     Difficulty: 2 Star

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