平衡二叉树结构,时间复杂度都是log(n) multiset, set, multimap, map multiset<T> st; insert, find, erase lower_bound, upper_bound map<int, string> m; m.insert(map<int, string>::value_type(num, str)); map<int, string>::iterator rec = m.begin(); rec = m.find(key) ; if(rec == m.end()) {} for( ; rec != m.end(); rec++)