includes用法

Question

vector<string> v1 = {"lelo","google","facebook","a"};
vector<string> v2 = {"google","facebook"};
if(includes(v1.begin(),v1.end(),v2.begin(),v2.end()))           cout<<"mou";

这个if为啥是false呢，v2是v1的子序列呀？

Answer 1

includes测试的是已排序的范围，参考http://www.cplusplus.com/reference/algorithm/includes/

Answer 2

std::includes 要求两个序列都是排过序的。