# LeetCode Notes: Min Stack

## Question

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

Implement the `MinStack` class:

• `MinStack()` initializes the stack object.
• `void push(val)` pushes the element `val` onto the stack.
• `void pop()` removes the element on the top of the stack.
• `int top()` gets the top element of the stack.
• `int getMin()` retrieves 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:

• -231 <= val <= 231 - 1
• Methods `pop`, `top` and `getMin` operations will always be called on non-empty stacks.
• At most 3 * 104 calls will be made to `push`, `pop`, `top`, and `getMin`.

## Solution

Analysis:

Use the array feature of javascript to operate, use the array to simulate a stack

Code:

``````/**
* initialize your data structure here.
*/
var MinStack = function() {
//Initialize an empty array
this.stack = []
};

/**
* @param {number} val
* @return {void}
*/
MinStack.prototype.push = function(val) {
this.stack.push(val)
};

/**
* @return {void}
*/
MinStack.prototype.pop = function() {
//Delete the last element
this.stack.splice(this.stack.length-1,1)
};

/**
* @return {number}
*/
MinStack.prototype.top = function() {
//Get the last element
return this.stack[this.stack.length-1]
};

/**
* @return {number}
*/
MinStack.prototype.getMin = function() {
return Math.min(...this.stack)
};

/**
* Your MinStack object will be instantiated and called as such:
* var obj = new MinStack()
* obj.push(val)
* obj.pop()
* var param_3 = obj.top()
* var param_4 = obj.getMin()
*/
``````