algorithm.h
反转
string:
string s=str;
reverse(s.begin()+2,s.begin()+7);//和下面一句效果一样
char[]
char str[]="abcdefgh";
reverse(str+2,str+7);
or
reverse(begin(str),begin(str)+7)
vector
reverse(begin(a), begin(a) + n);
reverse(begin(a), begin(a) + m);
reverse(begin(a) + m, begin(a) + n);