/*

    MinStack that supports push, pop, top, 

    and retrieving the minimum element in constant time.

*/

​

const MinStack = function() {

    this.stack = []

    this.min_stack = []

};

​

​

MinStack.prototype.push = function(val) {

    this.stack.push(val)

​

    if (this.min_stack.length === 0) {

        this.min_stack.push(val)

    } else {

        if (val <= this.min_stack[this.min_stack.length - 1]) {

            this.min_stack.push(val)

        }

    }

};

​

​

MinStack.prototype.pop = function() {

    if (this.stack.length > 0) {

        if (this.min_stack[this.min_stack.length - 1] === this.stack[this.stack.length - 1]) {

            this.min_stack.splice(-1,1)

        }

​

        this.stack.splice(-1,1)

    }

};

​

​

MinStack.prototype.top = function() {

    if (this.stack.length > 0) {

        return this.stack[this.stack.length - 1]

    }

​

    return 0

};

​

​

MinStack.prototype.getMin = function() {

    return this.min_stack.length === 0 ? [] : this.min_stack[this.min_stack.length - 1]

};

​

let minStack = new MinStack()

​

//  2, 0, -1, 4, 5, -2, 3, 2, 1, -5, 9, 8

minStack.push(2)

minStack.push(0)

minStack.push(-1)

minStack.push(4)

minStack.push(5)

minStack.push(-2)

minStack.push(3)

minStack.push(2)

minStack.push(1)

minStack.push(-5)

minStack.push(9)

minStack.push(8)

​

console.log(minStack.stack)     // [2, 0, -1, 4,  5, -2, 3,  2, 1, -5, 9, 8]

console.log(minStack.top())     // 8

console.log(minStack.getMin())  // -5

minStack.pop()

minStack.pop()

console.log(minStack.stack)     // [2, 0, -1, 4,  5,-2, 3,  2, 1, -5]

console.log(minStack.getMin())  // -5

minStack.pop()

console.log(minStack.getMin())  // -2

​