Loading problem...
You are analyzing telecom call-traffic logs across multiple cities.
The calls table stores one row per completed call event:
The combination (caller_id, recipient_id, call_time) is unique.
Task: For every city, find the hour(s) of day with the maximum number of calls. If a city has multiple hours tied at the same maximum, return all tied hours for that city.
Required output columns:
Required ordering:
Supported submission environments:
calls:
| caller_id | recipient_id | call_time | city |
|-----------|--------------|----------------------|----------|
| 8 | 4 | 2021-08-24 22:46:07 | Houston |
| 4 | 8 | 2021-08-24 22:57:13 | Houston |
| 5 | 1 | 2021-08-11 21:28:44 | Houston |
| 8 | 3 | 2021-08-17 22:04:15 | Houston |
| 11 | 3 | 2021-08-17 13:07:00 | New York |
| 8 | 11 | 2021-08-17 14:22:22 | New York |[
{"city":"Houston","peak_calling_hour":22,"number_of_calls":3},
{"city":"New York","peak_calling_hour":14,"number_of_calls":1},
{"city":"New York","peak_calling_hour":13,"number_of_calls":1}
]Explanation
Houston peaks at hour 22 with three calls. New York has a tie at hours 13 and 14, each with one call.
calls:
| caller_id | recipient_id | call_time | city |
|-----------|--------------|----------------------|---------|
| 1 | 9 | 2024-01-01 10:00:01 | Chicago |
| 2 | 8 | 2024-01-01 10:11:21 | Chicago |
| 3 | 7 | 2024-01-01 09:18:04 | Chicago |
| 4 | 6 | 2024-01-01 09:49:40 | Chicago |
| 5 | 5 | 2024-01-02 18:03:00 | Boston |
| 6 | 4 | 2024-01-02 18:11:00 | Boston |
| 7 | 3 | 2024-01-02 18:22:00 | Boston |[
{"city":"Boston","peak_calling_hour":18,"number_of_calls":3},
{"city":"Chicago","peak_calling_hour":10,"number_of_calls":2},
{"city":"Chicago","peak_calling_hour":9,"number_of_calls":2}
]Explanation
Chicago has a tie between 09 and 10 with two calls each. Boston peaks uniquely at 18 with three calls.
calls:
| caller_id | recipient_id | call_time | city |
|-----------|--------------|----------------------|----------|
| 90 | 91 | 2024-02-05 00:10:00 | San Jose |
| 92 | 93 | 2024-02-05 23:59:30 | San Jose |
| 94 | 95 | 2024-02-06 00:02:15 | San Jose |
| 96 | 97 | 2024-02-06 23:10:45 | San Jose |[
{"city":"San Jose","peak_calling_hour":23,"number_of_calls":2},
{"city":"San Jose","peak_calling_hour":0,"number_of_calls":2}
]Explanation
San Jose has an exact tie between hour 23 and hour 0 with two calls each.
Constraints