155. Min Stack

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.

• pop() -- Removes the element on top of the stack.

• top() -- Get the top element.

• getMin() -- Retrieve the minimum element in the stack.

Example 1:

Input
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

Output
[null,null,null,null,-3,null,0,-2]

Explanation
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); // return -3
minStack.pop();
minStack.top();    // return 0
minStack.getMin(); // return -2

class MinStack

=begin
    initialize your data structure here.
=end
    def initialize()
      @arry = []
      @min = nil
    end


=begin
    :type x: Integer
    :rtype: Void
=end
    def push(x)
      @arry.unshift(x)
    end


=begin
    :rtype: Void
=end
    def pop()
      @arry.delete_at(0)
    end


=begin
    :rtype: Integer
=end
    def top()
      @min = @arry.first
    end


=begin
    :rtype: Integer
=end
    def get_min()
      if @arry.size > 1
        if @min != nil
          if @min <= @arry[1..-1].min
            @min
          elsif
            @arry[1..-1].min
          end
        end
      end
      @arry.min
    end


end

# Your MinStack object will be instantiated and called as such:
# obj = MinStack.new()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.get_min()