0155-min-stack.js

/** 
 * https://leetcode.com/problems/min-stack
 * Time O(1) | Space O(N)
 * Your MinStack object will be instantiated and called as such:
 * var obj = new MinStack()
 * obj.push(x)
 * obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.getMin()
 */
class MinStack {
    /**
     * @constructor
     */
    constructor () {
        this.stack = [];
        this.minStack = [];
    }

    /**
     * @param {number} val
     * @return {void}
     */
    push (val, { minStack } = this) {
        this.stack.push(val);             /* Space O(N) */

        const isMinEmpty = !minStack.length;
        const hasNewMin = val <= this.top(minStack);
        const canAddMin = isMinEmpty || hasNewMin;
        if (canAddMin) minStack.push(val);/* Space O(N) */
    }

    /**
     * @return {void}
     */
    pop ({ stack, minStack } = this) {
        const top = stack.pop();          /* Time O(1) */

        const canPopMin = top === this.getMin();
        if (canPopMin) minStack.pop();    /* Time O(1) */
    }

    /**
     * @param {Array}
     * @return {number}
     */
    top (stack = this.stack) {
        return stack.length
            ? stack[stack.length - 1]     /* Time O(1) */
            : null;
    }

    /**
     * @return {number}
     */
    getMin (minStack = this.minStack) {
        return this.top(minStack);       /* Time O(1) */
    }
}


/** 
 * https://leetcode.com/problems/min-stack
 * Time O(1) | Space O(1)
 * Your MinStack object will be instantiated and called as such:
 * var obj = new MinStack()
 * obj.push(x)
 * obj.pop()
 * var param_3 = obj.top()
 * var param_4 = obj.getMin()
 */
class MinStack {
    constructor () {
        this.head = null
    }

    push (val) {
        this.head = (!this.head)   /* Space O(1) */
            ? new Node(val, val, null)
            : new Node(val, Math.min(val, this.head.min), this.head);
    }

    pop () {
        this.head = this.head.next;/* Time O(1) */
    }

    top () {
        return this.head.val;      /* Time O(1) */
    }

    getMin () {
        return this.head.min;      /* Time O(1) */
    }
}

class Node {
    constructor (val, min, next) {
        this.val = val;
        this.min = min;
        this.next = next;
    }
}