Add solution for Challenge 3 (#719)

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

Author: iamsurajmandal

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

@@ -0,0 +1,72 @@
+package main
+
+import "fmt"
+
+type Employee struct {
+	ID     int
+	Name   string
+	Age    int
+	Salary float64
+}
+
+type Manager struct {
+	Employees []Employee
+}
+
+// AddEmployee adds a new employee to the manager's list.
+func (m *Manager) AddEmployee(e Employee) {
+	// TODO: Implement this method
+	m.Employees = append(m.Employees,Employee{
+	    ID: e.ID,
+	    Name: e.Name, 
+	    Age: e.Age,
+	    Salary: e.Salary,
+	})
+}
+
+// RemoveEmployee removes an employee by ID from the manager's list.
+func (m *Manager) RemoveEmployee(id int) {
+	// TODO: Implement this method
+	for index, item := range m.Employees {
+	    if (item.ID == id) {
+	        m.Employees = append( m.Employees[:index],m.Employees[index + 1:]...)
+	    }
+	}
+}
+
+// GetAverageSalary calculates the average salary of all employees.
+func (m *Manager) GetAverageSalary() float64 {
+	sum := 0.000000 
+	if (len(m.Employees) < 1) {
+	    return sum
+	}
+	for _, item := range m.Employees {
+	    sum += item.Salary
+	}
+	return sum / float64(len(m.Employees))
+}
+
+// FindEmployeeByID finds and returns an employee by their ID.
+func (m *Manager) FindEmployeeByID(id int) *Employee {
+	for i := range m.Employees {
+		if m.Employees[i].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)
+	}
+}