Parse URL query parameters with flags and array values

Real coding interview question recently reported in group. Prompt: implement a function that receives a full URL and returns a map/object of query params. Level 1: parse basic key=value params separated by '&' after '?'. Level 2: params without values are boolean flags set to true. Level 3: comma-separated values become arrays/lists. Follow-ups discussed: duplicate keys, empty query strings, URL decoding, invalid formats, time complexity, space complexity, and clean extensible design. Contributor consented to anonymous save.