Twitch Software Development Engineer (SDE) interview questions

meeting on google doc, had a 15 mins intro section follow by 30 mins coding section , was asked a easy question but I missed a lot of edge cases

Design a search autocomplete system for a search engine. Users may input a sentence (at least one word and end with a special character '#'). For each character they type except '#', you need to return the top 3 historical hot sentences that have prefix the same as the part of sentence already typed. Here are the specific rules: