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

Constraints:

• Methods pop, top and getMin operations will always be called on non-empty stacks.

# @lc code=start
using LeetCode
Base.@kwdef struct MinStack{V<:Number}
    nums::Vector{V} = Int[]
    min_nums::Vector{V} = Int[]
end

function Base.push!(stack::MinStack, val::Int)::Nothing
    Base.push!(stack.nums, val)
    if isempty(stack.min_nums) || val <= stack.min_nums[end]
        Base.push!(stack.min_nums, val)
    end
    return nothing
end

function Base.pop!(stack::MinStack)::Nothing
    if Base.pop!(stack.nums) == stack.min_nums[end]
        Base.pop!(stack.min_nums)
    end
    return nothing
end

top(stack::MinStack)::Int = stack.nums[end]

get_min(stack::MinStack)::Int = stack.min_nums[end]
# @lc code=end

get_min (generic function with 1 method)

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