diff --git a/DIRECTORY.md b/DIRECTORY.md
index 8e5cb0d2..6fcb0090 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -23,6 +23,7 @@
       * [Test Is Valid Subsequence](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/arrays/subsequence/test_is_valid_subsequence.py)
   * Backtracking
     * Combination
+      * [Test Combination](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/backtracking/combination/test_combination.py)
       * [Test Combination 2](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/backtracking/combination/test_combination_2.py)
       * [Test Combination 3](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/backtracking/combination/test_combination_3.py)
     * Decode Message
@@ -139,6 +140,8 @@
       * [Test Can Visit All Rooms](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/graphs/keys_and_rooms/test_can_visit_all_rooms.py)
     * Knight On Chess Board
       * [Test Knight On Chess Board](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/graphs/knight_on_chess_board/test_knight_on_chess_board.py)
+    * Last Day Where You Can Still Cross
+      * [Test Last Day You Can Still Cross](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/graphs/last_day_where_you_can_still_cross/test_last_day_you_can_still_cross.py)
     * Maxareaofisland
       * [Test Max Area Of Island](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/graphs/maxareaofisland/test_max_area_of_island.py)
     * Min Cost To Supply
@@ -203,6 +206,8 @@
     * Ransom Note
       * [Test Ransom Note](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/hash_table/ransom_note/test_ransom_note.py)
   * Heap
+    * Construct Target With Sums
+      * [Test Construct Target With Sums](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/heap/construct_target_with_sums/test_construct_target_with_sums.py)
     * Kclosestelements
       * [Test Find K Closest Elements](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/heap/kclosestelements/test_find_k_closest_elements.py)
     * Longest Happy String
@@ -403,6 +408,8 @@
     * Topkfreqwords
       * [Test Top K Frequent Words](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/trie/topkfreqwords/test_top_k_frequent_words.py)
   * Two Pointers
+    * Append Chars To Make Subsequence
+      * [Test Append Chars To Make Subsequence](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/two_pointers/append_chars_to_make_subsequence/test_append_chars_to_make_subsequence.py)
     * Array 3 Pointers
       * [Test Array 3 Pointers](https://github.com/BrianLusina/PythonSnips/blob/master/algorithms/two_pointers/array_3_pointers/test_array_3_pointers.py)
     * Container With Most Water
@@ -600,6 +607,8 @@
   * Lrucache
     * [With Internal Linked List](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/lrucache/with_internal_linked_list.py)
     * [With Ordered Dict](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/lrucache/with_ordered_dict.py)
+  * Map Sum
+    * [Test Map Sum Pairs](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/map_sum/test_map_sum_pairs.py)
   * Orderedstream
     * [Test Ordered Stream](https://github.com/BrianLusina/PythonSnips/blob/master/datastructures/orderedstream/test_ordered_stream.py)
   * Queues
diff --git a/datastructures/map_sum/README.md b/datastructures/map_sum/README.md
new file mode 100644
index 00000000..e90f19cd
--- /dev/null
+++ b/datastructures/map_sum/README.md
@@ -0,0 +1,37 @@
+# Map Sum Pairs
+
+Design a data structure that supports the following operations:
+
+1. Insert a key-value pair:
+   - Each key is a string, and each value is an integer.
+   - If the key already exists, update its value to (overriding the previous value).
+
+2. Return the prefix sum:
+   - Given a string, `prefix`, return the total sum of all values associated with keys that start with this prefix.
+
+To accomplish this, implement a class MapSum:
+
+- Constructor: Initializes the object. 
+- `void insert (String key, int val)`: Inserts the key-value pair into the data structure. If the key already exists,
+  its value is updated to the new one. 
+- `int sum (String prefix)`: Returns the total sum of values for all keys that begin with the specified prefix.
+
+## Constraints
+
+- 1 ≤ `key.length`, `prefix.length` ≤ 50
+- Both `key` and `prefix` consist of only lowercase English letters.
+- 1 ≤ `val` ≤ 1000
+- At most 50 calls will be made to insert and sum.
+
+## Examples
+
+![Example 1](./images/examples/map_sum_pairs_example_1.png)
+![Example 2](./images/examples/map_sum_pairs_example_2.png)
+![Example 3](./images/examples/map_sum_pairs_example_3.png)
+
+## Topics
+
+- Hash Table
+- String
+- Design
+- Trie
diff --git a/datastructures/map_sum/__init__.py b/datastructures/map_sum/__init__.py
new file mode 100644
index 00000000..04490d99
--- /dev/null
+++ b/datastructures/map_sum/__init__.py
@@ -0,0 +1,129 @@
+from typing import Dict
+from collections import Counter
+
+from datastructures.trees.trie import TrieNode
+
+
+class MapSumBruteForce(object):
+    """
+    This solution to creating a map sum data structure that finds the sum of keys with a matching prefix uses a
+    Hash Table combined with Brute-Force Search and String Matching.
+
+    Time Complexity: Every insert operation is O(1). Every sum operation is O(N*P) where N is the number of items in the
+    map, and P is the length of the input prefix.
+
+    Space Complexity: The space used by map is linear in the size of all input key and val values combined.
+    """
+
+    def __init__(self):
+        self.mapping: Dict[str, int] = {}
+
+    def insert(self, key: str, val: int) -> None:
+        """
+        Inserts the key with the given value into the hash table
+        Args:
+            key (str): key to insert
+            val (int): value to insert
+        """
+        self.mapping[key] = val
+
+    def sum(self, prefix: str) -> int:
+        """
+        Finds the sum of all keys with the prefix `prefix`.
+        Args:
+            prefix (str): prefix to search for
+        Returns:
+            int: sum of all keys with the prefix `prefix`
+        """
+        running_sum = 0
+        for k, v in self.mapping.items():
+            if k.startswith(prefix):
+                running_sum += v
+
+        return running_sum
+
+
+class MapSumPrefix(object):
+    """
+    We can remember the answer for all possible prefixes in a HashMap score. When we get a new (key, val) pair, we
+    update every prefix of key appropriately: each prefix will be changed by delta = val - map[key], where map is the
+    previously associated value of key (zero if undefined.)
+
+    Time Complexity: Every insert operation is O(K^2), where K is the length of the key, as K strings are made of an
+    average length of K. Every sum operation is O(1).
+
+    Space Complexity: The space used by map is linear in the size of all input key and val values combined.
+    """
+
+    def __init__(self):
+        self.mapping: Dict[str, int] = {}
+        self.score = Counter()
+
+    def insert(self, key: str, val: int) -> None:
+        """
+        Inserts the key with the given value into the hash table
+        Args:
+            key (str): key to insert
+            val (int): value to insert
+        """
+        delta = val - self.mapping.get(key, 0)
+        self.mapping[key] = val
+        for i in range(len(key) + 1):
+            prefix = key[:i]
+            self.score[prefix] += delta
+
+    def sum(self, prefix: str) -> int:
+        """
+        Finds the sum of all keys with the prefix `prefix`.
+        Args:
+            prefix (str): prefix to search for
+        Returns:
+            int: sum of all keys with the prefix `prefix`
+        """
+        return self.score[prefix]
+
+
+class MapSumTrie(object):
+    """
+    Since we are dealing with prefixes, a Trie (prefix tree) is a natural data structure to approach this problem. For
+    every node of the trie corresponding to some prefix, we will remember the desired answer (score) and store it at
+    this node. As in the approach of using a prefix has map, this involves modifying each node by delta = val - map[key].
+
+    Time Complexity: Every insert operation is O(K), where K is the length of the key. Every sum operation is O(K).
+    Space Complexity: The space used is linear in the size of the total input.
+    """
+
+    def __init__(self):
+        self.mapping: Dict[str, int] = {}
+        self.score = Counter()
+        self.root = TrieNode()
+
+    def insert(self, key: str, val: int) -> None:
+        """
+        Inserts the key with the given value into the hash table
+        Args:
+            key (str): key to insert
+            val (int): value to insert
+        """
+        delta = val - self.mapping.get(key, 0)
+        self.mapping[key] = val
+        current = self.root
+        current.score += delta
+        for char in key:
+            current = current.children[char]
+            current.score += delta
+
+    def sum(self, prefix: str) -> int:
+        """
+        Finds the sum of all keys with the prefix `prefix`.
+        Args:
+            prefix (str): prefix to search for
+        Returns:
+            int: sum of all keys with the prefix `prefix`
+        """
+        current = self.root
+        for char in prefix:
+            if char not in current.children:
+                return 0
+            current = current.children[char]
+        return current.score
diff --git a/datastructures/map_sum/images/examples/map_sum_pairs_example_1.png b/datastructures/map_sum/images/examples/map_sum_pairs_example_1.png
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diff --git a/datastructures/map_sum/images/examples/map_sum_pairs_example_2.png b/datastructures/map_sum/images/examples/map_sum_pairs_example_2.png
new file mode 100644
index 00000000..773fafb9
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diff --git a/datastructures/map_sum/images/examples/map_sum_pairs_example_3.png b/datastructures/map_sum/images/examples/map_sum_pairs_example_3.png
new file mode 100644
index 00000000..e6f753f4
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diff --git a/datastructures/map_sum/test_map_sum_pairs.py b/datastructures/map_sum/test_map_sum_pairs.py
new file mode 100644
index 00000000..59e082f1
--- /dev/null
+++ b/datastructures/map_sum/test_map_sum_pairs.py
@@ -0,0 +1,110 @@
+import unittest
+from typing import Tuple, List
+from parameterized import parameterized
+from datastructures.map_sum import MapSumBruteForce, MapSumPrefix, MapSumTrie
+
+
+MAP_SUM_TEST_CASES = [
+    (
+        [
+            ("insert", ("apple", 3)),
+            ("sum", ("ap", 3)),
+            ("insert", ("apple", 2)),
+            ("sum", ("ap", 2)),
+        ],
+    ),
+    (
+        [
+            ("insert", ("apple", 3)),
+            ("sum", ("ap", 3)),
+            ("insert", ("ap", 2)),
+            ("sum", ("ap", 5)),
+        ],
+    ),
+    (
+        [
+            ("insert", ("apple", 3)),
+            ("insert", ("apple", 5)),
+            ("sum", ("ap", 5)),
+            ("insert", ("apricot", 2)),
+            ("sum", ("ap", 7)),
+        ],
+    ),
+    (
+        [
+            ("insert", ("car", 3)),
+            ("insert", ("cat", 2)),
+            ("insert", ("cart", 4)),
+            ("sum", ("ca", 9)),
+            ("sum", ("car", 7)),
+        ],
+    ),
+    (
+        [
+            ("insert", ("dog", 5)),
+            ("insert", ("cat", 7)),
+            ("sum", ("z", 0)),
+        ],
+    ),
+    (
+        [
+            ("insert", ("a", 3)),
+            ("insert", ("apple", 2)),
+            ("sum", ("a", 5)),
+            ("sum", ("app", 2)),
+        ],
+    ),
+]
+
+
+class MapSumPairsTestCase(unittest.TestCase):
+    @parameterized.expand(MAP_SUM_TEST_CASES)
+    def test_map_sum_pairs_brute_force(
+        self, operations: List[Tuple[str, Tuple[str, int]]]
+    ):
+        map_sum = MapSumBruteForce()
+        for operation in operations:
+            cmd = operation[0]
+            params = operation[1]
+            if cmd == "insert":
+                key, value = params
+                map_sum.insert(key, value)
+
+            if cmd == "sum":
+                prefix, expected = params
+                actual = map_sum.sum(prefix)
+                self.assertEqual(expected, actual)
+
+    @parameterized.expand(MAP_SUM_TEST_CASES)
+    def test_map_sum_pairs_prefix(self, operations: List[Tuple[str, Tuple[str, int]]]):
+        map_sum = MapSumPrefix()
+        for operation in operations:
+            cmd = operation[0]
+            params = operation[1]
+            if cmd == "insert":
+                key, value = params
+                map_sum.insert(key, value)
+
+            if cmd == "sum":
+                prefix, expected = params
+                actual = map_sum.sum(prefix)
+                self.assertEqual(expected, actual)
+
+    @parameterized.expand(MAP_SUM_TEST_CASES)
+    def test_map_sum_pairs_trie(self, operations: List[Tuple[str, Tuple[str, int]]]):
+        map_sum = MapSumTrie()
+        for operation in operations:
+            cmd = operation[0]
+            params = operation[1]
+            if cmd == "insert":
+                key, value = params
+                map_sum.insert(key, value)
+
+            if cmd == "sum":
+                prefix, expected = params
+                actual = map_sum.sum(prefix)
+                self.assertEqual(expected, actual)
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/datastructures/trees/trie/trie_node.py b/datastructures/trees/trie/trie_node.py
index 92d4413e..78761ace 100644
--- a/datastructures/trees/trie/trie_node.py
+++ b/datastructures/trees/trie/trie_node.py
@@ -4,11 +4,11 @@
 
 class TrieNode:
     def __init__(self):
-        # self.char = char
         """
         Initializes a TrieNode instance.
 
-        A TrieNode contains a character and a dictionary of its children. It also contains a boolean indicating whether the node is the end of a word in the Trie.
+        A TrieNode contains a character and a dictionary of its children. It also contains a boolean indicating whether
+        the node is the end of a word in the Trie.
 
         Parameters:
             None
@@ -19,6 +19,7 @@ def __init__(self):
         self.children: DefaultDict[str, TrieNode] = defaultdict(TrieNode)
         self.is_end = False
         self.index: Optional[int] = None
+        self.score: int = 0
 
     def __repr__(self):
         return f"TrieNode(index={self.index}, is_end={self.is_end})"
diff --git a/datastructures/trees/trie/word_dictionary/test_word_dictionary.py b/datastructures/trees/trie/word_dictionary/test_word_dictionary.py
index ba744e70..9fdc903e 100644
--- a/datastructures/trees/trie/word_dictionary/test_word_dictionary.py
+++ b/datastructures/trees/trie/word_dictionary/test_word_dictionary.py
@@ -29,6 +29,33 @@ def test_case_1(self):
         actual_get_words_two = word_dictionary.get_words()
         self.assertEqual(expected_words, actual_get_words_two)
 
+    def test_case_2(self):
+        word_dictionary = WordDictionary()
+        actual_words_1 = word_dictionary.get_words()
+        self.assertEqual([], actual_words_1)
+
+        word_dictionary.add_word("apple")
+        word_dictionary.add_word("grape")
+        actual_words_2 = word_dictionary.get_words()
+        expected_words_1 = ["apple", "grape"]
+        self.assertEqual(expected_words_1, actual_words_2)
+
+        actual_search_word_1 = word_dictionary.search_word("strawberry")
+        self.assertFalse(actual_search_word_1)
+
+        word_dictionary.add_word("banana")
+        word_dictionary.add_word("banan")
+
+        actual_search_word_2 = word_dictionary.search_word("bana..")
+        self.assertTrue(actual_search_word_2)
+
+        actual_search_word_3 = word_dictionary.search_word("ba...a")
+        self.assertTrue(actual_search_word_3)
+
+        actual_get_words_3 = word_dictionary.get_words()
+        expected_words_2 = ["apple", "banan", "banana", "grape"]
+        self.assertEqual(sorted(expected_words_2), sorted(actual_get_words_3))
+
 
 if __name__ == "__main__":
     unittest.main()