Count records by a property
Count objects by their string-valued property named key. Return [value,count] pairs ordered by the first occurrence of each value; treat property names literally, including __proto__. All input is valid JSON satisfying the constraints; do not mutate the meaning of values through type coercion. Interviewers use this problem to assess use a Map to avoid object prototype collisions and preserve insertion order.
Input
A JSON object {"items": [objects], "key": string}.
Output
Print one compact JSON value: an array of [string, integer] pairs.
Constraints
0 <= items length <= 10000; every item owns key with a string value of length <= 100; key length <= 100.
Example
Input
{"items":[{"team":"qa"},{"team":"dev"},{"team":"qa"}],"key":"team"}Output
[["qa",2],["dev",1]]
Example 2 input
{"items":[{"x":""},{"x":""}],"key":"x"}Output
[["",2]]
Boundary case: Do not use a plain object as an unguarded frequency table
Public test cases (2)
Input
{"items":[{"team":"qa"},{"team":"dev"},{"team":"qa"}],"key":"team"}Expected output
[["qa",2],["dev",1]]
Input
{"items":[{"x":"10"},{"x":"2"},{"x":"10"}],"key":"x"}Expected output
[["10",2],["2",1]]
Hints (2)
- Read the dynamic property with bracket notation
- Do not use a plain object as an unguarded frequency table
Target complexity: time O(n) · space O(g), with g distinct values