Group typed records by category
Group records by category into objects {category,ids}. Preserve first-seen category order and input id order within each group, including duplicate ids. Inputs are valid JSON and must not be modified unless the algorithm uses a local copy. This exercise probes typed data modeling, boundary handling, and algorithm selection.
Input
One JSON value: Item[]. See the sample for its exact shape.
Output
One compact JSON value of type Group[]. Strings include JSON quotes; arrays preserve the specified order.
Constraints
Array/string lengths are 0 to 10000 unless stated otherwise. Numbers are integers in [-1000000,1000000]; all computed results fit the safe integer range.
Example
Input
[{"id":1,"category":"qa"},{"id":2,"category":"dev"},{"id":3,"category":"qa"}]Output
[{"category":"qa","ids":[1,3]},{"category":"dev","ids":[2]}]Example 2 input
[{"id":4,"category":"b"},{"id":3,"category":"a"}]Output
[{"category":"b","ids":[4]},{"category":"a","ids":[3]}]Checks a boundary or contrasting case beyond the public examples.
Public test cases (2)
Input
[{"id":1,"category":"qa"},{"id":2,"category":"dev"},{"id":3,"category":"qa"}]Expected output
[{"category":"qa","ids":[1,3]},{"category":"dev","ids":[2]}]Input
[]
Expected output
[]
Hints (2)
- Start with the required output order and the empty-input behavior.
- Map each category to the index of its output group
Target complexity: time O(n) · space O(n)