java 一个例子

import java.util.*;public class Main { publicstatic void main(String args[]){System.out.println(fun(100));}public static int fun(int n){Stack<Integer> stack=new Stack();stack.push(0);Integer sum=0;int pos=0;while(!stack.empty()){if(pos++<n)stack.push(pos);elsesum+=stack.pop();}return sum;} }