feat: tree order statistics was updated

LuchoBazz · web-flow · commit e5d7ec1ffe1f · 2022-08-24T15:15:22.000-05:00
diff --git a/data_structure/data_structure_tree_order_statistic.cpp b/data_structure/data_structure_tree_order_statistic.cpp
@@ -9,21 +9,35 @@ using __gnu_pbds::rb_tree_tag;
 using __gnu_pbds::tree_order_statistics_node_update;
 using __gnu_pbds::null_type;
 
+// _GLIBCXX_DEBUG must not be defined otherwise some internal check will fail
+#undef _GLIBCXX_DEBUG
+
 template <typename K, typename V, typename Comp = less<K>>
 using indexed_map = tree<K, V, Comp, rb_tree_tag, tree_order_statistics_node_update>;
 
 template <typename K, typename Comp = less<K>>
 using indexed_set = indexed_map<K, null_type, Comp>;
 
+// ¡¡IMPORTANT!! (for using less_equals<K>)
 // using less_equals<K> makes lower_bound works as upper_bound and vice-versa
+// for erase use: any.erase(any.find_by_order(any.order_of_key(val)));
+// don't use .find() because it will always return .end()
 template <typename K, typename V, typename Comp = less_equal<K>>
 using indexed_multimap = indexed_map<K, V, Comp>;
 
 template <typename K, typename Comp = less_equal<K>>
 using indexed_multiset = indexed_map<K, null_type, Comp>;
 
+// Reference: https://codeforces.com/blog/entry/11080
+
 // Usage
+// 1) Return the value of the idx index
 //    auto it = any.find_by_order(idx); (0-indexed)
 //    (*it).first, (*it).second
+// 2) Get the index of the key value
 //    int index = any.order_of_key(key);
-//    {1: 10, 2 :20,  5: 50}, order_of_key(3) -> return index 2
+//    {1: 10, 2 :20,  5: 50}
+//    any.order_of_key(2) -> return index 1
+//    any.order_of_key(3) -> return index 2
+// 3) Correct way to use erase:
+//    any.erase(any.find_by_order(any.order_of_key(val)));
