LESSON 401 OF 404 · PROJECTS: OBJECT-ORIENTED

Stack: Build a MyStack Class (Go) in Go

Practice

A stack is a pile where you only touch the top: the last value you put in is the first one you take out (LIFO, last in, first out), like a pile of plates. Build a class MyStack that stores whole numbers in a data []int slice inside type MyStack struct and offers four operations.

The methods:

func (stack *MyStack) push(value int)
func (stack *MyStack) pop() int
func (stack MyStack) peek() int
func (stack MyStack) size() int

Rules:

push puts the value on top of the stack. It returns nothing.
pop removes the top value (the one pushed last) and returns it.
peek returns the top value but leaves it on the stack, so the size does not change.
size returns how many values are on the stack. A new stack has size 0, and after popping everything the size is 0 again.
The stack keeps working after it becomes empty: you can push again.
Calling pop or peek on an empty stack is not part of this exercise and the tests never do it. (In Go, indexing an empty slice panics.)

You start with: The starter already contains the code that uses your stack (below).

stack := MyStack{}
stack.push(10)
stack.push(20)
stack.push(30)
fmt.Println("Top: " + strconv.Itoa(stack.peek()))
fmt.Println("Size: " + strconv.Itoa(stack.size()))
fmt.Println("Pop: " + strconv.Itoa(stack.pop()))
fmt.Println("Size: " + strconv.Itoa(stack.size()))
fmt.Println("Pop: " + strconv.Itoa(stack.pop()))
fmt.Println("Pop: " + strconv.Itoa(stack.pop()))
fmt.Println("Empty size: " + strconv.Itoa(stack.size()))
stack.push(7)
fmt.Println("Top: " + strconv.Itoa(stack.peek()))
fmt.Println("Size: " + strconv.Itoa(stack.size()))

Expected output:

Top: 30
Size: 3
Pop: 30
Size: 2
Pop: 20
Pop: 10
Empty size: 0
Top: 7
Size: 1

Reading the output: after pushing 10, 20 and 30 the top is 30 and the size 3. Popping gives 30, leaving size 2. Two more pops give 20 and then 10 (last in, first out), the stack is empty (size 0), and after pushing 7 the top is 7 and the size 1.

The top of the stack is the end of the list: adding and removing at the end is fast, and the last value pushed is always the last element.

Go has no classes: the struct holds the data and methods are functions with a receiver. push and pop change the slice, so they use a pointer receiver (*MyStack). Use append to add and stack.data[:len(stack.data)-1] to drop the last element.

type MyStack struct {
	data []int
}

func (stack *MyStack) push(value int) {
	stack.data = append(stack.data, value)
}

func (stack *MyStack) pop() int {
	top := stack.data[len(stack.data)-1]
	stack.data = stack.data[:len(stack.data)-1]
	return top
}

func (stack MyStack) peek() int {
	return stack.data[len(stack.data)-1]
}

func (stack MyStack) size() int {
	return len(stack.data)
}

STEP 1 OF 12

Guided

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Stack: Build a MyStack Class (Go) in Go

Stack Impl in Go