Instructor Distinct Subject Count

Easy

A university analytics team stores teaching assignments in the Teacher table: teacher_id: identifier of the instructor subject_id: identifier of the subject dept_id: identifier of the department where that subject is offered Data rule: (subject_id, dept_id) is unique in the table. A teacher can still appear multiple times for the same subject_id when that subject is taught in different departments. Task: For each teacher_id, compute how many distinct subject_id values that teacher teaches. Output requirements: Return exactly two columns: teacher_id, cnt cnt is the number of unique subject_id values per teacher Output order is not important Supported submission environments: SQL (SQLite 3.27.2) Pandas (Python)

Example 1

Input

Teacher:
| teacher_id | subject_id | dept_id |
|------------|------------|---------|
| 1          | 2          | 3       |
| 1          | 2          | 4       |
| 1          | 3          | 3       |
| 2          | 1          | 1       |
| 2          | 2          | 1       |
| 2          | 3          | 1       |
| 2          | 4          | 1       |

Output

[
  {"teacher_id":1,"cnt":2},
  {"teacher_id":2,"cnt":4}
]

Explanation

Teacher 1 appears twice for subject 2 in different departments, but that subject is counted once. Teacher 2 teaches four different subjects.

Example 2

Input

Teacher:
| teacher_id | subject_id | dept_id |
|------------|------------|---------|
| 10         | 100        | 1       |
| 10         | 100        | 2       |
| 10         | 101        | 3       |
| 11         | 100        | 3       |
| 11         | 102        | 4       |
| 12         | 103        | 5       |
| 12         | 103        | 6       |

Output

[
  {"teacher_id":10,"cnt":2},
  {"teacher_id":11,"cnt":2},
  {"teacher_id":12,"cnt":1}
]

Explanation

Shared subject IDs across different teachers are counted independently for each teacher.

Example 3

Input

Teacher:
| teacher_id | subject_id | dept_id |
|------------|------------|---------|
| 42         | 900        | 10      |
| 42         | 901        | 10      |
| 42         | 902        | 11      |
| 42         | 900        | 12      |

Output

[
  {"teacher_id":42,"cnt":3}
]

Explanation

Even with four assignment rows, subject 900 is duplicated for the same teacher and contributes only one unique subject.

Constraints

0 <= number of rows in Teacher <= 10000
1 <= teacher_id <= 2000000000
1 <= subject_id <= 2000000000
1 <= dept_id <= 2000000000
(subject_id, dept_id) is unique
A teacher may have multiple rows with the same subject_id across departments
Return columns exactly as: teacher_id, cnt
For SQL submissions, use SQLite 3.27.2 semantics
For Pandas submissions, return a DataFrame with columns: teacher_id, cnt

Teacher: | teacher_id | subject_id | dept_id | |------------|------------|---------| | 1 | 2 | 3 | | 1 | 2 | 4 | | 1 | 3 | 3 | | 2 | 1 | 1 | | 2 | 2 | 1 | | 2 | 3 | 1 | | 2 | 4 | 1 |

Teacher: | teacher_id | subject_id | dept_id | |------------|------------|---------| | 10 | 100 | 1 | | 10 | 100 | 2 | | 10 | 101 | 3 | | 11 | 100 | 3 | | 11 | 102 | 4 | | 12 | 103 | 5 | | 12 | 103 | 6 |

Teacher: | teacher_id | subject_id | dept_id | |------------|------------|---------| | 42 | 900 | 10 | | 42 | 901 | 10 | | 42 | 902 | 11 | | 42 | 900 | 12 |