C++ STL 算法：根据第n个元素排序

1、nth_element(b,n,e)//排序好后取出前n个

nth_element(ideq.begin(),ideq.begin()+3,ideq.end());//默认从小到大

2、nth_element(b,n,e,p)

nth_element(ideq.begin(),ideq.begin()+3,ideq.end(),greater<int>());