Stack

Implement a stack data structure in JavaScript that contains the following operations:

Constructor

Stack

Creates an instance of a Stack class that doesn't contain any items. The constructor not accept any arguments.

Methods

push

Pushes an item onto the top of the stack.

• Arguments
  • {*} item: The item to be pushed onto the stack.
• Returns
  • {number}: The new length of the stack.
• Time Complexity
  • O(1)

pop

Remove an item at the top of the stack.

• Returns
  • {*} item: The item at the top of the stack if it is not empty, undefined otherwise.
• Time Complexity
  • O(1)

isEmpty

Determines if the stack is empty.

• Returns
  • {boolean}: true if the stack has no items, false otherwise.
• Time Complexity
  • O(1)

peek

Returns the item at the top of the stack without removing it from the stack.

• Returns
  • {*}: The item at the top of the stack if it is not empty, undefined otherwise.
• Time Complexity
  • O(1)

length

Returns the number of items in the stack.

• Returns
  • {number}: The number of items in the stack.
• Time Complexity
  • O(1)

Examples

const stack = new Stack();
stack.isEmpty(); // true
stack.push(1);
stack.push(2);
stack.length(); // 2
stack.push(3);
stack.peek(); // 3
stack.pop(); // 3
stack.isEmpty(); // false