Find the team size

# Table: Employee
# 
# +---------------+---------+
# | Column Name   | Type    |
# +---------------+---------+
# | employee_id   | int     |
# | team_id       | int     |
# +---------------+---------+
# employee_id is the primary key (column with unique values) for this table.
# Each row of this table contains the ID of each employee and their respective team.
# 
#  
# 
# Write a solution to find the team size of each of the employees.
# 
# Return the result table in any order.
# 
# The result format is in the following example.
#
# Example 1:
# Input:
# Employee Table:
# +-------------+------------+
# | employee_id | team_id    |
# +-------------+------------+
# |     1       |     8      |
# |     2       |     8      |
# |     3       |     8      |
# |     4       |     7      |
# |     5       |     9      |
# |     6       |     9      |
# +-------------+------------+
# Output:
# +-------------+------------+
# | employee_id | team_size  |
# +-------------+------------+
# |     1       |     3      |
# |     2       |     3      |
# |     3       |     3      |
# |     4       |     1      |
# |     5       |     2      |
# |     6       |     2      |
# +-------------+------------+
# Explanation:
# Employees with Id 1,2,3 are part of a team with team_id = 8.
# Employee with Id 4 is part of a team with team_id = 7.
# Employees with Id 5,6 are part of a team with team_id = 9.

import pandas as pd

def team_size(employee: pd.DataFrame) -> pd.DataFrame:
  team_counts = employee.groupby('team_id')['employee_id'].transform('count')
  employee['team_size'] = team_counts
  return employee[['employee_id', 'team_size']]