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Second phone interview: design a social media platform to share pictures (basically Instagram). What SQL queries would you run to get posts from a particular user, or to get all the users who haven't posted anything before?
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Backend Engineer

Interviewed at Graphika

4.5★
Dec 13, 2020

Second phone interview: design a social media platform to share pictures (basically Instagram). What SQL queries would you run to get posts from a particular user, or to get all the users who haven't posted anything before?

first round: Design an **Autocomplete System** that provides the **top 10 most-searched words** based on a given prefix. 1. **Insert a Word:** Utilize a **Trie** structure, storing words and their frequencies at the leaf nodes. 2. **Retrieve Suggestions:** Traverse the Trie for the prefix, then apply a **max-heap** to track the top 10 words by frequency. 3. **Time Complexity:** - **Insertion:** O(L), where L is the length of the word. - **Search:** O(P + K log K), where P is the length of the prefix and K is the number of suggestions. Example: For the prefix **"ap"**, suggestions may include: `apple (50)`, `app (40)`, `apricot (30)`, `application (20)`. high level design, without coding second round was to design a system that relates to blockchain, to fetch transaction from it and to find specific details in specific blocks, store it on a db and fetch it from there in future searches (not sure the interviewer was 100% sure about the specifications of the system)
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backend devops developer

Interviewed at Dcentralab

4.5★
Jan 14, 2025

first round: Design an **Autocomplete System** that provides the **top 10 most-searched words** based on a given prefix. 1. **Insert a Word:** Utilize a **Trie** structure, storing words and their frequencies at the leaf nodes. 2. **Retrieve Suggestions:** Traverse the Trie for the prefix, then apply a **max-heap** to track the top 10 words by frequency. 3. **Time Complexity:** - **Insertion:** O(L), where L is the length of the word. - **Search:** O(P + K log K), where P is the length of the prefix and K is the number of suggestions. Example: For the prefix **"ap"**, suggestions may include: `apple (50)`, `app (40)`, `apricot (30)`, `application (20)`. high level design, without coding second round was to design a system that relates to blockchain, to fetch transaction from it and to find specific details in specific blocks, store it on a db and fetch it from there in future searches (not sure the interviewer was 100% sure about the specifications of the system)

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