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ISL 2022 C1

  • Answer

A ±1\pm 1-sequence is a sequence of 2022 numbers a1,…,a2022a_{1}, \ldots, a_{2022}, each equal to either +1 or -1 . Determine the largest CC so that, for any ±1\pm 1-sequence, there exists an integer kk and indices 1⩽t1<…<tk⩽20221 \leqslant t_{1}<\ldots<t_{k} \leqslant 2022 so that ti+1−ti⩽2t_{i+1}-t_{i} \leqslant 2 for all ii, and ∣∑i=1kati∣⩾C\left|\sum_{i=1}^{k} a_{t_{i}}\right| \geqslant C (Czech Republic)

Official text Transcription from NuminaMath olympiads, checked word for word against the official paper. Quoted with source.

Official text: IMO 2022 Shortlist booklet, page 6.

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Solutions

Official solution Solution 1 by the IMO Problem Selection Committee

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