Lean4

16. Run-length encoding

MediumProgramAcademy Pass20 points

Run-length encoding replaces each run of equal, adjacent characters by the character and the length of the run. Write rle s, the encoding of the string s as a list of pairs.

For "aaabcc" the runs are three 'a', one 'b' and two 'c'.

Examples

  1. Inputrle "aaabcc"Output[('a', 3), ('b', 1), ('c', 2)]
  2. Inputrle ""Output[]

Submitting also runs 5 hidden tests.

Constraints

  • Upper- and lower-case letters are different characters.
stringslistsrecursion

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Solution.lean
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3#guard (rle "aaabcc") = ([('a', 3), ('b', 1), ('c', 2)])
4#guard (rle "") = ([])
examples

Run checks your code against the examples and your custom inputs and records nothing. Submit also runs the hidden tests, confirms the axioms your proof uses and records the result. Each uses one compiler check.

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