#1 3.3 Stack of Plates implementation

README.md

@@ -40,7 +40,7 @@ Solving programming questions from ["Cracking the Coding Interview 6th Edition"]
 |---|-------------------------------|:-------------:|:---------:|
 |3.1| [Three in one][39]            | [tests][40]   |     ✓     |
 |3.2| [Stack Min][41]               | [tests][42]   |     ✓     |
-|3.3| Stack of Plates               | tests         |           |
+|3.3| [Stack of Plates][43]         | [tests][44]   |     ✓     |
 |3.4| Queue via Stacks              | tests         |           |
 |3.5| Sort Stack                    | tests         |           |
 |3.6| Animal Shelter                | tests         |           |
@@ -87,3 +87,5 @@ Solving programming questions from ["Cracking the Coding Interview 6th Edition"]
 [40]:  ch03/01_three_in_one_test.go
 [41]:  ch03/02_stack_min.go
 [42]:  ch03/02_stack_min_test.go
+[43]:  ch03/03_stack_of_plates.go
+[44]:  ch03/03_stack_of_plates_test.go

ch03/03_stack_of_plates.go

@@ -0,0 +1,135 @@
+package ch03
+
+import (
+	"errors"
+)
+
+// StackSet represents set of fixed (capped) stacks
+type StackSet struct {
+	stacks []*FixedStack
+}
+
+// Pop returns (and removes) the top item from the top stack
+// If the top stack is empty, it will be removed from the set
+func (set *StackSet) Pop() (int, error) {
+	stack, err := set.topStack()
+	if err != nil {
+		return 0, err
+	}
+
+	value, err := stack.Pop()
+	if err != nil {
+		return 0, err
+	}
+
+	if stack.IsEmpty() {
+		set.removeStack()
+	}
+
+	return value, nil
+}
+
+// Push add an item to the top stack
+// If the top stack is full, new stack will be created
+// and appended to the set
+func (set *StackSet) Push(data int) error {
+	stack, err := set.topStack()
+	if err != nil {
+		stack = set.appendStack()
+	}
+
+	if stack.IsFull() {
+		stack = set.appendStack()
+	}
+
+	return stack.Push(data)
+}
+
+// TopStack returns the top stack from the set
+func (set *StackSet) topStack() (*FixedStack, error) {
+	n := len(set.stacks) - 1
+	if n < 0 {
+		return nil, errors.New("set is empty")
+	}
+
+	return set.stacks[n], nil
+}
+
+// AppendStack adds a new stack to the set
+func (set *StackSet) appendStack() *FixedStack {
+	stack := NewFixedStack(3)
+	set.stacks = append(set.stacks, stack)
+
+	return stack
+}
+
+// RemoveStack removes top stack from the set
+func (set *StackSet) removeStack() {
+	n := len(set.stacks) - 1
+	if n >= 0 {
+		set.stacks = set.stacks[:n]
+	}
+}
+
+// FixedStack is a capped stack (stack length is limited to cap)
+type FixedStack struct {
+	top *Item
+	len int
+	cap int
+}
+
+// NewFixedStack desc
+func NewFixedStack(cap int) *FixedStack {
+	stack := new(FixedStack)
+	stack.len = 0
+	stack.cap = cap
+
+	return stack
+}
+
+// Pop returns (and removes) the top item from the stack
+func (stack *FixedStack) Pop() (int, error) {
+	if stack.IsEmpty() {
+		return 0, errors.New("empty stack error")
+	}
+
+	top := stack.top
+	stack.top = top.next
+	stack.len--
+
+	return top.data, nil
+}
+
+// Push add an item to the stack
+func (stack *FixedStack) Push(data int) error {
+	if stack.IsFull() {
+		return errors.New("full stack error")
+	}
+
+	top := New(data)
+	top.next = stack.top
+
+	stack.top = top
+	stack.len++
+
+	return nil
+}
+
+// Peek returns the top item from the satck (without removing it)
+func (stack *FixedStack) Peek() (int, error) {
+	if stack.top == nil {
+		return 0, errors.New("empty Stack error")
+	}
+
+	return stack.top.data, nil
+}
+
+// IsEmpty returns true when stack is empty, false otherwise
+func (stack *FixedStack) IsEmpty() bool {
+	return stack.top == nil
+}
+
+// IsFull returns true when stack is its max capacity, false otherwise
+func (stack *FixedStack) IsFull() bool {
+	return stack.cap == stack.len
+}