這是4月份快手前端實習筆試的一道程式設計題，要求是實現：

入棧：NumberStack.push(num) 、出棧：NumberStack.pop() 、找出棧中第n大的數：NumberStack.max(n)

//下面是我的版本
function NumberStack() {
  this.stack = []; //棧的定義
}

NumberStack.prototype.push = function (num) {
  if (typeof num != "number") return false;
  this.stack.push(num);
};

NumberStack.prototype.pop = function
 
 () {
  if(this.stack.length>0){
    let last = this.stack.pop();
    return last;
  }
};

NumberStack.prototype.max = function (n) {
  let newArr = [].concat(this.stack);
  return newArr.sort()[n-1];
};

另外下面是在牛客網上另一個朋友寫的，我覺得比我得要好一些

function NumberStack(){
    this.stack=[];//儲存棧
    this.maxStack=[];//輔助棧，從小到大的排序
 

}
NumberStack.prototype.push=function(num){
    if(Object.prototype.toString.call(num)!="object Number") return false; 
    this.stack.push(num); 
    if(!this.maxStack.length){ 
        this.maxStack.push(num);
    }else{
        let len=his.maxStack.length;
        for(let i=0;i<len;i++){
            if
 
(num<this.maxStack[i]){
                this.maxStack.splice(i,0,num);//將num插入maxStack到合適的位置
                break; 
            }
        }
    }
} 
NumberStack.prototype.pop=function(){ 
    let num=this.stack.pop();
    this.maxStack.splice(this.maxStack.indexOf(num),1);//將num從maxStack中刪除 
    return num;
}

NumberStack.prototype.max=function(n){ 
    if(n<1||n>this.maxStack.length) return false; 
    return this.maxStack[this.maxStack.length-n];
}