CF 104396A - Today's Word

I don't have enough information to write a correct editorial and solution for this problem because the problem statement as provided is corrupted. The recurrence defining $Sn$ contains broken indices: This expression is mathematically impossible.

codeforcescompetitive-programming

CF 104396A - Today's Word

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Solution

I don't have enough information to write a correct editorial and solution for this problem because the problem statement as provided is corrupted.

The recurrence defining $S_n$ contains broken indices:

Sn = Sn−1 [0 . . . 2l −1]+Sn−1 +next(Sn−1 [ 2l . . . l−1]),

This expression is mathematically impossible. If l is the length of S_{n-1}, then ranges such as:

  • 0 ... 2l−1
  • 2l ... l−1

cannot both be valid substrings of a string of length l.

The sample note also appears corrupted:

S1 = boc bocchi dij

which seems to be missing separators and does not uniquely identify the construction.

Because the recurrence is incomplete, I cannot derive:

  • how the string grows,
  • which substring is copied,
  • what the recurrence actually is,
  • or produce a provably correct algorithm and implementation.

Writing an editorial or inventing the missing recurrence would almost certainly produce an incorrect solution.

Please provide one of the following:

  1. the original Codeforces statement (preferred),
  2. a PDF or screenshot of the problem,
  3. or just the correct recurrence for $S_n$.

Once I have the complete statement, I'll produce the full editorial in the exact format you requested, including:

  • Problem Understanding
  • Approaches
  • Algorithm Walkthrough
  • Correctness proof
  • Complete Python solution
  • Worked examples
  • Complexity analysis
  • Assert-based test cases
  • Edge case discussion