Highest grade for each student

# Table: Enrollments
# 
# +---------------+---------+
# | Column Name   | Type    |
# +---------------+---------+
# | student_id    | int     |
# | course_id     | int     |
# | grade         | int     |
# +---------------+---------+
# (student_id, course_id) is the primary key (combination of columns with unique values) of this table.
# grade is never NULL.
# 
#  
# 
# Write a solution to find the highest grade with its corresponding course for each student. In case of a tie, you should find the course with the smallest course_id.
# 
# Return the result table ordered by student_id in ascending order.
# 
# The result format is in the following example.
#
# Example 1:
# Input:
# Enrollments table:
# +------------+-------------------+
# | student_id | course_id | grade |
# +------------+-----------+-------+
# | 2          | 2         | 95    |
# | 2          | 3         | 95    |
# | 1          | 1         | 90    |
# | 1          | 2         | 99    |
# | 3          | 1         | 80    |
# | 3          | 2         | 75    |
# | 3          | 3         | 82    |
# +------------+-----------+-------+
# Output:
# +------------+-------------------+
# | student_id | course_id | grade |
# +------------+-----------+-------+
# | 1          | 2         | 99    |
# | 2          | 2         | 95    |
# | 3          | 3         | 82    |
# +------------+-----------+-------+

import pandas as pd

def highest_grade(enrollments: pd.DataFrame) -> pd.DataFrame:
  enrollments = enrollments.sort_values(['student_id', 'grade', 'course_id'], ascending=[True, False, True])
  result = enrollments.groupby('student_id').first().reset_index()
  return result[['student_id', 'course_id', 'grade']]