CF 106298A - Explosive String
The statement as provided is incomplete in a way that makes the actual task undefined. All we know is that the input contains a string with characters from {L, R, ?} and that we are allowed to replace every ‘?’ either with ‘L’ or with ‘R’.
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Solve time: 29s
Verified: no
Solution
The statement as provided is incomplete in a way that makes the actual task undefined.
All we know is that the input contains a string with characters from {L, R, ?} and that we are allowed to replace every ‘?’ either with ‘L’ or with ‘R’. What is missing is the objective function: what makes one resulting string better than another, or what property we are supposed to compute after the replacements.
Without that, there is no well-defined optimal strategy. For example, if the goal were to maximize adjacent equal pairs, then the optimal construction would differ completely from a case where we maximize alternating transitions, minimize runs, check lexicographically smallest outcome, or satisfy constraints involving substrings. Each of these leads to a different solution, and the correct editorial depends entirely on that missing condition.
If you can provide the full statement (especially the part describing what makes a valid or optimal “explosive string”), I can write the complete Codeforces-style editorial in the format you requested, including the algorithm derivation, proof, and implementation.