Here you can watch how I solved A–F from Hello 2024: https://youtu.be/3TV2VpVbUjM. Unfortunately, I only solved 1919E - Counting Prefixes after the contest has ended because my C++ template was too poor. This is an important lesson for me to collect all important algorithms and finally sit down and include them in the template.
UPD: the video is high resolution now.
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