Update README.md

Author: XuhuaHuang

StandardTemplateLibrary/README.md

@@ -1,5 +1,18 @@
 # `StandardTemplateLibrary`
 
+## Data Structures
+
+| Container                    | Implementation                            | Lookup       | Insertion     | Deletion     |
+|-----------------------------|--------------------------------------------|--------------|----------------|--------------|
+| `std::list`                 | Doubly linked list                         | O(n)         | O(1) (with iterator) | O(1) (with iterator) |
+| `std::forward_list`         | Singly linked list                         | O(n)         | O(1) (after node) | O(1) (after node) |
+| `std::vector`               | Dynamic array (contiguous)                 | O(1) (random access) / O(n) (search) | O(1) amortized at end / O(n) elsewhere | O(n) |
+| `std::deque`                | Double-ended queue (blocks)                | O(1) (random access) | O(1) at front/back | O(1) at front/back |
+| `std::set`, `std::map`      | Balanced binary tree (Red-Black tree)      | O(log n)     | O(log n)       | O(log n)     |
+| `std::unordered_set`, `std::unordered_map` | Hash table                  | O(1) average / O(n) worst | O(1) avg / O(n) worst | O(1) avg / O(n) worst |
+| `std::multiset`, `std::multimap` | Balanced binary tree (Red-Black tree) | O(log n)     | O(log n)       | O(log n)     |
+| `std::unordered_multiset`, `std::unordered_multimap` | Hash table        | O(1) average / O(n) worst | O(1) avg / O(n) worst | O(1) avg / O(n) worst |
+
 ##  **Quick Algorithm Lookup Table**
 
 | What You Want to Know                                                           |     On a Unsorted Range     |    On a Sorted Range   |   With a set or map  |      With a multiset or multimap      |