25Practical coding: build a web crawler, start simple, then make it concurrent and safe.▼mediumNewGoogleMicrosoftAmazon◆ premiumA classic coding round with a security twist: the crawler fetches URLs that strangers wrote. The scored answer gets concurrency right, then adds scope, limits and SSRF protection.Open full answer →
35A gift card can be redeemed twice if two requests arrive at the same moment. Explain the bug class and fix it properly.▼hardNewAmazonMicrosoftSalesforce◆ premiumEvery check passed and every write succeeded. The money still left twice, because the check and the write were two steps and another request got between them.Open full answer →