155.最小栈.js

/*
 * @lc app=leetcode.cn id=155 lang=javascript
 *
 * [155] 最小栈
 */

// @lc code=start
/**
 * initialize your data structure here.
 */
var MinStack = function() {
  this.stack = [];
  this._minStack = [];
};

/**
 * @param {number} x
 * @return {void}
 */
MinStack.prototype.push = function(x) {
  let minTop = this._minStack[this._minStack.length - 1];
  if (minTop === undefined || minTop >= x) {
    this._minStack.push(x);
  }
  this.stack.push(x);
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
  let top = this.stack.pop();
  let minTop = this._minStack[this._minStack.length - 1];
  if (top === minTop) {
    this._minStack.pop();
  }
};

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

/**
 * @return {number}
 */
MinStack.prototype.getMin = function() {
  return this._minStack[this._minStack.length - 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()
 */
// @lc code=end