//基于平衡树AVL实现，O(lgn)
//有序
set[HTML_REMOVED] a:
map[HTML_REMOVED] b:不能有重复元素
multiset[HTML_REMOVED] c:
multimap<[HTML_REMOVED] d: 可以有重复元素

//基于哈希表实现，O(1)
//无序
unordered_set[HTML_REMOVED]
unordered_map[HTML_REMOVED]
unoredred_multiset[HTML_REMOVED]
unordered_multimap[HTML_REMOVED]