155_min_stack.js

// tags: #stack

// https://leetcode.cn/problems/min-stack/

// time: 96ms | beat 82%
var MinStack = function () {
  this.min = null;
  this.stack = [];
};

/**
 * @param {number} val
 * @return {void}
 */
MinStack.prototype.push = function (val) {
  // need call stack.length before stack.push
  if (!this.stack.length) this.min = val;
  else this.min = Math.min(this.min, val);
  this.stack.push(val);
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function () {
  const val = this.stack.pop();
  if (val === this.min) {
    this.min = Math.min(...this.stack);
  }
};

/**
 * @return {number}
 */
MinStack.prototype.top = function () {
  return this.stack.at(-1);
};

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

/**
 * 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()
 */