Add solution for Challenge 3 (#1106)

Co-authored-by: go-interview-practice-bot[bot] <230190823+go-interview-practice-bot[bot]@users.noreply.github.com>

Author: jrab66

challenge-3/submissions/jrab66/solution-template.go

@@ -0,0 +1,61 @@
+package main
+
+import "fmt"
+
+type Employee struct {
+	ID     int
+	Name   string
+	Age    int
+	Salary float64
+}
+
+type Manager struct {
+	Employees []Employee
+}
+
+func (m *Manager) AddEmployee(e Employee) {
+	m.Employees = append(m.Employees, e)
+}
+
+func (m *Manager) RemoveEmployee(id int) {
+	for i := len(m.Employees) - 1; i >= 0; i-- {
+		e := m.Employees[i]
+		if e.ID == id {
+			m.Employees = append(m.Employees[:i], m.Employees[i+1:]...)
+		}
+	}
+}
+
+func (m *Manager) GetAverageSalary() float64 {
+	if len(m.Employees) == 0 {
+		return 0.0
+	}
+
+	avg := 0.0
+	for _, e := range m.Employees {
+		avg += e.Salary
+	}
+	return avg / float64(len(m.Employees))
+}
+func (m *Manager) FindEmployeeByID(id int) *Employee {
+	for i, e := range m.Employees {
+		if e.ID == id {
+			return &m.Employees[i]
+		}
+	}
+	return nil
+}
+
+func main() {
+	manager := Manager{}
+	manager.AddEmployee(Employee{ID: 1, Name: "Alice", Age: 30, Salary: 70000})
+	manager.AddEmployee(Employee{ID: 2, Name: "Bob", Age: 25, Salary: 65000})
+	manager.RemoveEmployee(1)
+	averageSalary := manager.GetAverageSalary()
+	employee := manager.FindEmployeeByID(2)
+
+	fmt.Printf("Average Salary: %f\n", averageSalary)
+	if employee != nil {
+		fmt.Printf("Employee found: %+v\n", *employee)
+	}
+}