added "1670. Design Front Middle Back Queue"

Author: fluttermiddlepodcast

README.md

@@ -5,7 +5,7 @@ Solutions from [LeetCode](https://leetcode.com) on Dart.
 ## Easy
 
 | Name                                        | LeetCode                                                                     | Solution                                                      |
-|---------------------------------------------|------------------------------------------------------------------------------|---------------------------------------------------------------|
+| ------------------------------------------- | ---------------------------------------------------------------------------- | ------------------------------------------------------------- |
 | 9. Palindrome Number                        | [Link](https://leetcode.com/problems/palindrome-number/)                     | [Link](./lib/easy/palindrome_number.dart)                     |
 | 26. Remove Duplicates from Sorted Array     | [Link](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)   | [Link](./lib/easy/remove_duplicates_from_sorted_array.dart)   |
 | 27. Remove Element                          | [Link](https://leetcode.com/problems/remove-element/)                        | [Link](./lib/easy/remove_element.dart)                        |
@@ -33,16 +33,17 @@ Solutions from [LeetCode](https://leetcode.com) on Dart.
 ## Medium
 
 | Name                                   | LeetCode                                                                | Solution                                                   |
-|----------------------------------------|-------------------------------------------------------------------------|------------------------------------------------------------|
+| -------------------------------------- | ----------------------------------------------------------------------- | ---------------------------------------------------------- |
 | 12. Integer to Roman                   | [Link](https://leetcode.com/problems/integer-to-roman/)                 | [Link](./lib/medium/integer_to_roman.dart)                 |
 | 222. Count Complete Tree Nodes         | [Link](https://leetcode.com/problems/count-complete-tree-nodes/)        | [Link](./lib/medium/count_complete_tree_nodes.dart)        |
 | 230. Kth Smallest Element in a BST     | [Link](https://leetcode.com/problems/kth-smallest-element-in-a-bst/)    | [Link](./lib/medium/kth_smallest_element_in_a_bst.dart)    |
 | 328. Odd Even Linked List              | [Link](https://leetcode.com/problems/odd-even-linked-list/)             | [Link](./lib/medium/odd_even_linked_list.dart)             |
 | 1325. Delete Leaves With a Given Value | [Link](https://leetcode.com/problems/delete-leaves-with-a-given-value/) | [Link](./lib/medium/delete_leaves_with_a_given_value.dart) |
+| 1670. Design Front Middle Back Queue   | [Link](https://leetcode.com/problems/design-front-middle-back-queue/)   | [Link](./lib/medium/design_front_middle_back_queue.dart)   |
 
 ## Hard
 
 | Name                          | LeetCode                                                         | Solution                                          |
-|-------------------------------|------------------------------------------------------------------|---------------------------------------------------|
+| ----------------------------- | ---------------------------------------------------------------- | ------------------------------------------------- |
 | 23. Merge k Sorted Lists      | [Link](https://leetcode.com/problems/merge-k-sorted-lists/)      | [Link](./lib/hard/merge_k_sorted_lists.dart)      |
 | 32. Longest Valid Parentheses | [Link](https://leetcode.com/problems/longest-valid-parentheses/) | [Link](./lib/hard/longest_valid_parentheses.dart) |

lib/medium/design_front_middle_back_queue.dart

@@ -0,0 +1,42 @@
+class FrontMiddleBackQueue {
+  final _list = [];
+
+  void pushFront(int val) {
+    _list.insert(0, val);
+  }
+
+  void pushMiddle(int val) {
+    _list.insert(_list.length ~/ 2, val);
+  }
+
+  void pushBack(int val) {
+    _list.add(val);
+  }
+
+  int popFront() {
+    if (_list.isEmpty) {
+      return -1;
+    }
+
+    return _list.removeAt(0);
+  }
+
+  int popMiddle() {
+    if (_list.isEmpty) {
+      return -1;
+    }
+
+    var size = _list.length;
+    var index = size % 2 == 0 ? size ~/ 2 - 1 : size ~/ 2;
+
+    return _list.removeAt(index);
+  }
+
+  int popBack() {
+    if (_list.isEmpty) {
+      return -1;
+    }
+
+    return _list.removeLast();
+  }
+}

test/medium/design_front_middle_back_queue_test.dart

@@ -0,0 +1,26 @@
+import 'package:leetcode_dart/medium/design_front_middle_back_queue.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group(
+    'Example tests',
+    () {
+      test(
+        'Example test',
+        () {
+          FrontMiddleBackQueue q = FrontMiddleBackQueue();
+          q.pushFront(1);
+          q.pushBack(2);
+          q.pushMiddle(3);
+          q.pushMiddle(4);
+
+          expect(1, q.popFront());
+          expect(3, q.popMiddle());
+          expect(4, q.popMiddle());
+          expect(2, q.popBack());
+          expect(-1, q.popFront());
+        },
+      );
+    },
+  );
+}