155. 最小栈

设计一个支持 push ，pop ，top 操作，并能在常数时间内检索到最小元素的栈。

实现 MinStack 类:

• MinStack() 初始化堆栈对象。
• void push(int val) 将元素 val 推入堆栈。
• void pop() 删除堆栈顶部的元素。
• int top() 获取堆栈顶部的元素。
• int getMin() 获取堆栈中的最小元素。

示例

输入：
["MinStack","push","push","push","getMin","pop","top","getMin"]
[[],[-2],[0],[-3],[],[],[],[]]

输出：
[null,null,null,null,-3,null,0,-2]

解释：
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> 返回 -3.
minStack.pop();
minStack.top(); --> 返回 0.
minStack.getMin(); --> 返回 -2.

答案

for 遍历

var MinStack = function() {
  this.items = []
};

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

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
  this.items.pop()
};

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

/**
 * @return {number}
 */
MinStack.prototype.getMin = function() {
  if(this.items.length < 0){return undefined}
  let result = this.items[0]
  for(let i=0;i<this.items.length;i++){
    const element = this.items[i]
    if(result > element){
      result = element
    }
  }
  return result
};


const minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
console.log(minStack.getMin()) //返回 -3.
minStack.pop();
console.log(minStack.top()) //返回 0.
console.log(minStack.getMin())  //返回 -2.

console.log(minStack)

最小栈

空间换时间

var MinStack = function() {
  this.items = []
  this.mins = []
};

/**
 * @param {number} val
 * @return {void}
 */
MinStack.prototype.push = function(val) {
  this.items.push(val)
  let min = this.mins.length > 0
  ?
      val < this.mins[this.mins.length-1] ? val : this.mins[this.mins.length-1]
  :
      val

  this.mins.push(min)
};

/**
 * @return {void}
 */
MinStack.prototype.pop = function() {
  this.items.pop()
  this.mins.pop()
};

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

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