Add solution for Challenge 3 (#848)

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

Author: cckwes

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

@@ -0,0 +1,78 @@
+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) {
+    m.Employees = append(m.Employees, e)
+}
+
+// RemoveEmployee removes an employee by ID from the manager's list.
+func (m *Manager) RemoveEmployee(id int) {
+	foundIndex := m.findEmployeeIndexByID(id)
+	if foundIndex == -1 {
+	    return
+	}
+	
+	m.Employees = append(m.Employees[:foundIndex], m.Employees[foundIndex+1:]...)
+}
+
+// GetAverageSalary calculates the average salary of all employees.
+func (m *Manager) GetAverageSalary() float64 {
+    if len(m.Employees) == 0 {
+        return 0
+    }
+    
+	totalSalary := 0.0
+	
+	for _, v := range m.Employees {
+	    totalSalary += v.Salary
+	}
+	
+	return totalSalary / float64(len(m.Employees))
+}
+
+// FindEmployeeByID finds and returns an employee by their ID.
+func (m *Manager) FindEmployeeByID(id int) *Employee {
+	foundIndex := m.findEmployeeIndexByID(id)
+	if foundIndex == -1 {
+	    return nil
+	}
+	
+	return &m.Employees[foundIndex]
+}
+
+func (m *Manager) findEmployeeIndexByID(id int) int {
+    for index, v := range m.Employees {
+        if v.ID == id {
+            return index
+        }
+    }
+    
+    return -1
+}
+
+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)
+	}
+}