Stack

  • Stack is like stacking plates in your Kitchen.
  • Last in, first out: LIFO
  • In Ruby, you can treat an array as stack because there is push and pop methods.
  • But what about peek? Java has peek, what about Ruby?
  • You can use .last instead of peek. And it will return the item on the top.
  • .length or .size will return the size of the Stack.
stack = []
stack << 1 # push 1 => stack = [1]
stack << 2 # push 2 => stack = [1, 2]
stack.pop # pop => 2, stack = [1]

push#

  • There are many ways to push items on a stack in Ruby:
[88] pry(main)> stack
=> [1, 2, 3]
[89] pry(main)> stack.push(4)
=> [1, 2, 3, 4]
[90] pry(main)> stack.push 5
=> [1, 2, 3, 4, 5]
[91] pry(main)> stack << 6
=> [1, 2, 3, 4, 5, 6]
[92] pry(main)> stack
=> [1, 2, 3, 4, 5, 6]

pop#

  • Removes an item from the end, and returns that item
[74] pry(main)> stack
=> [1, 2, 3]
[75] pry(main)> stack.pop
=> 3
[76] pry(main)> stack
=> [1, 2]

delete item from the front#

  • Shift deletes the item from the front and returns that item.
  • Useful when Array is used as a Queue.
[127] pry(main)> nums
=> [1, 2, 3]
[128] pry(main)> nums.shift
=> 1
[129] pry(main)> nums
=> [2, 3]

last ( instead of peek )#

[79] pry(main)> stack
=> [1, 2, 3]
[80] pry(main)> stack.last
=> 3

size/length/count#

  • Size, count, length returns the same result.
  • Check the article on size, count and length to learn more about their differences.
[84] pry(main)> stack
=> [1, 2, 3]
[85] pry(main)> stack.size
=> 3
[86] pry(main)> stack.count
=> 3
[87] pry(main)> stack.length
=> 3

Related LeetCode problem:#

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