diff --git a/src/main/java/Collections/Practice/CollectionBasics.java b/src/main/java/Collections/Practice/CollectionBasics.java
index e45cb49..b7c0e24 100644
--- a/src/main/java/Collections/Practice/CollectionBasics.java
+++ b/src/main/java/Collections/Practice/CollectionBasics.java
@@ -33,6 +33,9 @@ public static int sum(Collection<Integer> numbers) {
         // TODO:
         // Loop through the collection
         // Add each number to total
+        for (Integer num : numbers) {
+            total += num;
+        }
 
         return total;
     }
@@ -48,7 +51,12 @@ public static int countEven(Collection<Integer> numbers) {
 
         // TODO:
         // Loop through the collection
+        for (Integer num : numbers) {
         // If the number is even, increase count
+        if (num % 2 == 0) {
+            count++;
+        }
+    }
 
         return count;
     }
@@ -64,7 +72,13 @@ public static int findMax(Collection<Integer> numbers) {
 
         // TODO:
         // Loop through numbers
+        for (Integer num : numbers) {
         // Update max if current number is larger
+            if (num > max) {
+                max = num;
+            }
+        }
+
 
         return max;
     }
@@ -77,10 +91,15 @@ public static int findMax(Collection<Integer> numbers) {
     */
     public static boolean hasDuplicates(Collection<Integer> numbers) {
 
+
+
+
         // TODO:
         // Hint:
         // Compare the size of a collection with the size of a Set
 
+
+
         return false;
     }
 
@@ -96,6 +115,11 @@ public static int countOccurrences(Collection<Integer> numbers, int target) {
         // TODO:
         // Loop through numbers
         // If number equals target, increase count
+        for (Integer num : numbers) {
+            if (num == target) {
+                count++;
+            }
+        }
 
         return count;
     }
@@ -112,8 +136,15 @@ public static Collection<Integer> filterGreaterThanTwenty(Collection<Integer> nu
 
         // TODO:
         // Loop through numbers
-        // Add numbers greater than 20 to result
+        for (Integer num : numbers) {
+            // Add numbers greater than 20 to result
+            if (num > 20) {
+                result.add(num);
+
+            }
+        }
+
 
         return result;
     }
-}
+    }
diff --git a/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java b/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
index 6c2f4e1..7a62729 100644
--- a/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
+++ b/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
@@ -1,15 +1,28 @@
 package CollectionsHackerrank;
 
+import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 import java.util.Queue;
+import java.util.Set;
+import java.util.ArrayList;
+import java.util.LinkedHashSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Stack;
+
 
 public class CollectionsHackerrankProblems {
-    public class CollectionsHackerrankPractice {
+    public static class CollectionsHackerrankPractice {
 
         public static void main(String[] args) {
 
             // You can test your methods here
+            List<Integer> numbers = Arrays.asList(1,2,2,3,4,4,5);
+            System.out.println(removeDuplicates(numbers));
+        }
+
+
 
         }
 
@@ -24,8 +37,14 @@ public static void main(String[] args) {
         public static List<Integer> removeDuplicates(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Set<Integer> uniqueNumbers = new LinkedHashSet<>(numbers); // removes duplicates
+            List<Integer> result = new ArrayList<>(uniqueNumbers);
+
+
+
+
+            return result;
 
-            return null;
         }
 
         /*
@@ -39,10 +58,22 @@ public static List<Integer> removeDuplicates(List<Integer> numbers) {
         public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Map<Integer, Integer> frequencyMap = new HashMap<>();
 
-            return null;
+            for (Integer num : numbers) {
+                if (frequencyMap.containsKey(num)) {
+                    frequencyMap.put(num, frequencyMap.get(num) + 1);
+                } else {
+                    frequencyMap.put(num, 1);
+                }
+            }
+
+            return frequencyMap;
         }
 
+
+
+
         /*
         Problem 3
         Return the first number that appears only once.
@@ -54,6 +85,18 @@ public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
         public static Integer firstUnique(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Map<Integer, Integer> frequencyMap = new HashMap<>();
+
+            for (Integer num : numbers) {
+                frequencyMap.put(num, frequencyMap.getOrDefault(num, 0) + 1);
+            }
+
+            for (Integer num : numbers) {
+                if (frequencyMap.get(num) == 1) {
+                    return num;
+                }
+            }
+
 
             return null;
         }
@@ -71,10 +114,23 @@ public static Integer firstUnique(List<Integer> numbers) {
         public static boolean twoSum(List<Integer> numbers, int target) {
 
             // TODO: Implement this method
+            Set<Integer> seen = new HashSet<>();
+
+            for (int num : numbers) {
+                int complement = target - num;
+
+                if (seen.contains(complement)) {
+                    return true;
+                }
+
+                seen.add(num);
+            }
 
             return false;
         }
 
+
+
         /*
         Problem 5
         Count how many unique words exist in a list.
@@ -86,10 +142,16 @@ public static boolean twoSum(List<Integer> numbers, int target) {
         public static int countUniqueWords(List<String> words) {
 
             // TODO: Implement this method
+            Set<String> uniqueWords = new HashSet<>();
+
+            for (String word : words) {
+                uniqueWords.add(word);
+            }
 
-            return 0;
+            return uniqueWords.size();
         }
 
+
         /*
         Problem 6
         Reverse a queue.
@@ -101,10 +163,23 @@ public static int countUniqueWords(List<String> words) {
         public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
 
             // TODO: Implement this method
+            Stack<Integer> stack = new Stack<>();
 
-            return null;
+            // Move elements from queue to stack
+            while (!queue.isEmpty()) {
+                stack.push(queue.poll());
+            }
+
+            // Move elements back to queue
+            while (!stack.isEmpty()) {
+                queue.add(stack.pop());
+            }
+
+            return queue;
         }
 
+
+
         /*
         Problem 7
         Determine whether parentheses are balanced.
@@ -119,10 +194,28 @@ public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
         public static boolean isBalanced(String expression) {
 
             // TODO: Implement this method
+            Stack<Character> stack = new Stack<>();
 
-            return false;
+            for (char c : expression.toCharArray()) {
+
+                if (c == '(') {
+                    stack.push(c);
+                }
+                else if (c == ')') {
+
+                    if (stack.isEmpty()) {
+                        return false;
+                    }
+
+                    stack.pop();
+                }
+            }
+
+            return stack.isEmpty();
         }
 
+
+
         /*
         Problem 8
         Return the number that appears most frequently in the list.
@@ -134,10 +227,27 @@ public static boolean isBalanced(String expression) {
         public static Integer mostFrequent(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Map<Integer, Integer> frequency = new HashMap<>();
 
-            return null;
+            for (Integer num : numbers) {
+                frequency.put(num, frequency.getOrDefault(num, 0) + 1);
+            }
+
+            int maxCount = 0;
+            Integer result = null;
+
+            for (Map.Entry<Integer, Integer> entry : frequency.entrySet()) {
+                if (entry.getValue() > maxCount) {
+                    maxCount = entry.getValue();
+                    result = entry.getKey();
+                }
+            }
+
+            return result;
         }
 
+
+
         /*
         Problem 9
         Group words based on their length.
@@ -154,10 +264,24 @@ public static Integer mostFrequent(List<Integer> numbers) {
         public static Map<Integer, List<String>> groupByLength(List<String> words) {
 
             // TODO: Implement this method
+            Map<Integer, List<String>> map = new HashMap<>();
 
-            return null;
+            for (String word : words) {
+
+                int length = word.length();
+
+                if (!map.containsKey(length)) {
+                    map.put(length, new ArrayList<>());
+                }
+
+                map.get(length).add(word);
+            }
+
+            return map;
         }
 
+
+
         /*
         Problem 10
         Return the maximum sum of any window of size k.
@@ -171,8 +295,26 @@ public static Map<Integer, List<String>> groupByLength(List<String> words) {
         public static int maxSlidingWindowSum(List<Integer> numbers, int k) {
 
             // TODO: Implement this method
+            int windowSum = 0;
 
-            return 0;
+            // First window
+            for (int i = 0; i < k; i++) {
+                windowSum += numbers.get(i);
+            }
+
+            int maxSum = windowSum;
+
+            // Slide the window
+            for (int i = k; i < numbers.size(); i++) {
+                windowSum += numbers.get(i);       // add next
+                windowSum -= numbers.get(i - k);   // remove previous
+                maxSum = Math.max(maxSum, windowSum);
+            }
+
+            return maxSum;
         }
+
+
+
     }
-}
+
diff --git a/src/main/java/Iterable/Examples/ForEachLoopDemo.java b/src/main/java/Iterable/Examples/ForEachLoopDemo.java
index a6d2198..4c79ebd 100644
--- a/src/main/java/Iterable/Examples/ForEachLoopDemo.java
+++ b/src/main/java/Iterable/Examples/ForEachLoopDemo.java
@@ -17,12 +17,20 @@ public static void main(String[] args) {
 
         // TODO:
         // Use a for-each loop to print each student name
+        for (String student : students) {
+            System.out.println(student);
+        }
+
 
 
         System.out.println("\nPrinting students in uppercase:");
 
         // TODO:
         // Use a for-each loop to print each name in uppercase
+        for (String student : students) {
+            System.out.println(student.toUpperCase());
+        }
+
 
 
         System.out.println("\nCount the number of students:");
@@ -31,6 +39,11 @@ public static void main(String[] args) {
 
         // TODO:
         // Use a for-each loop to count how many students are in the list
+        for (String student : students) {
+            System.out.println(student.toUpperCase());
+        }
+
+
 
         System.out.println("Total students: " + count);
     }
diff --git a/src/main/java/Iterable/Examples/IteratorDemo.java b/src/main/java/Iterable/Examples/IteratorDemo.java
index b09fca7..6003ccd 100644
--- a/src/main/java/Iterable/Examples/IteratorDemo.java
+++ b/src/main/java/Iterable/Examples/IteratorDemo.java
@@ -26,6 +26,11 @@ public static void main(String[] args) {
         // TODO:
         // Use iterator.hasNext() and iterator.next()
         // Print each number
+        while (iterator.hasNext()) {
+            Integer number = iterator.next();
+            System.out.println(number);
+        }
+
 
 
         System.out.println("\nRemoving odd numbers using Iterator");
@@ -35,6 +40,13 @@ public static void main(String[] args) {
         // TODO:
         // Use iterator to remove odd numbers
         // Remember: use iterator.remove()
+        while (iterator.hasNext()) {
+            Integer number = iterator.next();
+
+            if (number % 2 != 0) {
+                iterator.remove();
+            }
+        }
 
 
         System.out.println("\nUpdated list:");
diff --git a/src/main/java/Iterable/Practice/IterableWarmups.java b/src/main/java/Iterable/Practice/IterableWarmups.java
index 9e9de94..84cc06a 100644
--- a/src/main/java/Iterable/Practice/IterableWarmups.java
+++ b/src/main/java/Iterable/Practice/IterableWarmups.java
@@ -30,6 +30,9 @@ public static int sum(Iterable<Integer> numbers) {
 
         // TODO:
         // Use a for-each loop to calculate the sum
+        for (Integer num : numbers) {
+            total += num;
+        }
 
         return total;
     }
@@ -46,11 +49,18 @@ public static int countEven(Iterable<Integer> numbers) {
         // TODO:
         // Loop through numbers
         // Increment count if number is even
+        for (Integer num : numbers) {
+            if (num % 2 == 0) {
+                count++;
+            }
+        }
 
         return count;
     }
 
 
+
+
     /*
     PROBLEM 3
     Return the maximum value
@@ -62,11 +72,18 @@ public static int findMax(Iterable<Integer> numbers) {
         // TODO:
         // Loop through numbers
         // Update max if current number is larger
+        for (Integer num : numbers) {
+            if (num > max) {
+                max = num;
+            }
+        }
 
         return max;
     }
 
 
+
+
     /*
     PROBLEM 4 (BONUS)
     Count how many times a word appears
@@ -78,7 +95,14 @@ public static int countMatches(Iterable<String> words, String target) {
         // TODO:
         // Loop through words
         // Compare each word to target
+        for (String word : words) {
+            if (word.equals(target)) {
+                count++;
+            }
+        }
 
         return count;
     }
+
+
 }
diff --git a/src/main/java/Lists/ArrayLists/ArrayListProblems.java b/src/main/java/Lists/ArrayLists/ArrayListProblems.java
index baf4dfa..97d5f2d 100644
--- a/src/main/java/Lists/ArrayLists/ArrayListProblems.java
+++ b/src/main/java/Lists/ArrayLists/ArrayListProblems.java
@@ -34,10 +34,21 @@ public static void main(String[] args) {
     public static int sum(List<Integer> nums) {
 
         // TODO: Implement this method
+        int total = 0;
 
-        return 0;
+        for (int num : nums) {
+            total += num;
+        }
+
+        return total;
     }
 
+
+
+
+
+
+
     /*
     Problem 2
     Count how many EVEN numbers exist in the list.
@@ -49,10 +60,19 @@ public static int sum(List<Integer> nums) {
     public static int countEvens(List<Integer> nums) {
 
         // TODO: Implement this method
+        int count = 0;
+
+        for (int num : nums) {
+            if (num % 2 == 0) {
+                count++;
+            }
+        }
 
-        return 0;
+        return count;
     }
 
+
+
     /*
     Problem 3
     Determine if the list contains any duplicate values.
@@ -67,10 +87,19 @@ public static int countEvens(List<Integer> nums) {
     public static boolean hasDuplicate(List<Integer> nums) {
 
         // TODO: Implement this method
+        for (int i = 0; i < nums.size(); i++) {
+            for (int j = i + 1; j < nums.size(); j++) {
+                if (nums.get(i).equals(nums.get(j))) {
+                    return true;
+                }
+            }
+        }
 
         return false;
     }
 
+
+
     /*
     Problem 4
     Return the largest number in the list.
@@ -82,10 +111,19 @@ public static boolean hasDuplicate(List<Integer> nums) {
     public static int findMax(List<Integer> nums) {
 
         // TODO: Implement this method
+        int max = nums.get(0);
+
+        for (int num : nums) {
+            if (num > max) {
+                max = num;
+            }
+        }
 
-        return 0;
+        return max;
     }
 
+
+
     /*
     Problem 5
     Return a NEW list that contains the elements of the original list in reverse order.
@@ -100,6 +138,14 @@ public static List<Integer> reverse(List<Integer> nums) {
 
         // TODO: Implement this method
 
-        return null;
+        List<Integer> reversed = new ArrayList<>();
+
+        for (int i = nums.size() - 1; i >= 0; i--) {
+            reversed.add(nums.get(i));
+        }
+
+        return reversed;
     }
+
+
 }
diff --git a/src/main/java/Lists/LinkedLists/LinkedListProblems.java b/src/main/java/Lists/LinkedLists/LinkedListProblems.java
index 178a2ba..885edaf 100644
--- a/src/main/java/Lists/LinkedLists/LinkedListProblems.java
+++ b/src/main/java/Lists/LinkedLists/LinkedListProblems.java
@@ -38,6 +38,8 @@ public static void main(String[] args) {
     public static void addToFront(LinkedList<Integer> list, int value) {
 
         // TODO: Implement this method
+        list.addFirst(value);
+
 
     }
 
@@ -52,6 +54,7 @@ public static void addToFront(LinkedList<Integer> list, int value) {
     public static void addToEnd(LinkedList<Integer> list, int value) {
 
         // TODO: Implement this method
+        list.addLast(value);
 
     }
 
@@ -66,7 +69,7 @@ public static void addToEnd(LinkedList<Integer> list, int value) {
     public static void removeFirstElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
-
+        list.removeFirst();
     }
 
     /*
@@ -80,7 +83,7 @@ public static void removeFirstElement(LinkedList<Integer> list) {
     public static void removeLastElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
-
+        list.removeLast();
     }
 
     /*
@@ -94,6 +97,9 @@ public static void removeLastElement(LinkedList<Integer> list) {
     public static int getFirstElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
+        if (!list.isEmpty()) {
+            list.removeLast();
+        }
 
         return 0;
     }
@@ -109,7 +115,9 @@ public static int getFirstElement(LinkedList<Integer> list) {
     public static int getLastElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
-
-        return 0;
+        return list.getLast();
     }
+
+
+
 }
diff --git a/src/main/java/Maps/HashMap/HashMapProblems.java b/src/main/java/Maps/HashMap/HashMapProblems.java
index 04b5567..9f7f26d 100644
--- a/src/main/java/Maps/HashMap/HashMapProblems.java
+++ b/src/main/java/Maps/HashMap/HashMapProblems.java
@@ -35,9 +35,11 @@ public static void main(String[] args) {
     public static void addItem(Map<String, Integer> map, String item, int quantity) {
 
         // TODO: Implement this method
-
+        map.put(item, quantity);
     }
 
+
+
     /*
     Problem 2
     Return the quantity of a specific item.
@@ -49,10 +51,11 @@ public static void addItem(Map<String, Integer> map, String item, int quantity)
     public static int getQuantity(Map<String, Integer> map, String item) {
 
         // TODO: Implement this method
-
-        return 0;
+        return map.get(item);
     }
 
+
+
     /*
     Problem 3
     Update the quantity of an existing item.
@@ -64,9 +67,11 @@ public static int getQuantity(Map<String, Integer> map, String item) {
     public static void updateQuantity(Map<String, Integer> map, String item, int newQuantity) {
 
         // TODO: Implement this method
-
+        map.put(item, newQuantity);
     }
 
+
+
     /*
     Problem 4
     Remove an item from the map.
@@ -78,9 +83,11 @@ public static void updateQuantity(Map<String, Integer> map, String item, int new
     public static void removeItem(Map<String, Integer> map, String item) {
 
         // TODO: Implement this method
-
+        map.remove(item);
     }
 
+
+
     /*
     Problem 5
     Count how many times each number appears in a list.
@@ -92,7 +99,18 @@ public static void removeItem(Map<String, Integer> map, String item) {
     public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
 
         // TODO: Implement this method
+        Map<Integer, Integer> frequencyMap = new HashMap<>();
 
-        return null;
+        for (Integer num : numbers) {
+            if (frequencyMap.containsKey(num)) {
+                frequencyMap.put(num, frequencyMap.get(num) + 1);
+            } else {
+                frequencyMap.put(num, 1);
+            }
+        }
+
+        return frequencyMap;
     }
+
+
 }
diff --git a/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java b/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
index e8bbdc2..de87a7c 100644
--- a/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
+++ b/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
@@ -33,9 +33,11 @@ public static void main(String[] args) {
     public static void addStudent(Map<String, Integer> map, String name, int grade) {
 
         // TODO: Implement this method
-
+        map.put(name, grade);
     }
 
+
+
     /*
     Problem 2
     Update the grade of an existing student.
@@ -47,9 +49,11 @@ public static void addStudent(Map<String, Integer> map, String name, int grade)
     public static void updateGrade(Map<String, Integer> map, String name, int newGrade) {
 
         // TODO: Implement this method
-
+        map.put(name, newGrade);
     }
 
+
+
     /*
     Problem 3
     Remove a student from the LinkedHashMap.
@@ -61,9 +65,11 @@ public static void updateGrade(Map<String, Integer> map, String name, int newGra
     public static void removeStudent(Map<String, Integer> map, String name) {
 
         // TODO: Implement this method
-
+        map.remove(name);
     }
 
+
+
     /*
     Problem 4
     Return the first student inserted into the LinkedHashMap.
@@ -75,10 +81,11 @@ public static void removeStudent(Map<String, Integer> map, String name) {
     public static String getFirstInserted(Map<String, Integer> map) {
 
         // TODO: Implement this method
-
-        return null;
+        return map.keySet().iterator().next();
     }
 
+
+
     /*
     Problem 5
     Given a list of words, return a LinkedHashMap that counts
@@ -91,7 +98,14 @@ public static String getFirstInserted(Map<String, Integer> map) {
     public static Map<String, Integer> wordFrequency(List<String> words) {
 
         // TODO: Implement this method
+        Map<String, Integer> map = new LinkedHashMap<>();
 
-        return null;
+        for (String word : words) {
+            map.put(word, map.getOrDefault(word, 0) + 1);
+        }
+
+        return map;
     }
+
+
 }
diff --git a/src/main/java/Maps/TreeMap/TreeMapProblems.java b/src/main/java/Maps/TreeMap/TreeMapProblems.java
index b101d2e..beb28ce 100644
--- a/src/main/java/Maps/TreeMap/TreeMapProblems.java
+++ b/src/main/java/Maps/TreeMap/TreeMapProblems.java
@@ -31,9 +31,11 @@ public static void main(String[] args) {
     public static void addPlayer(TreeMap<Integer, String> map, int rank, String name) {
 
         // TODO: Implement this method
-
+        map.put(rank, name);
     }
 
+
+
     /*
     Problem 2
     Return the player with the highest ranking (smallest key).
@@ -45,10 +47,11 @@ Return the player with the highest ranking (smallest key).
     public static String getTopPlayer(TreeMap<Integer, String> map) {
 
         // TODO: Implement this method
-
-        return null;
+        return map.get(map.firstKey());
     }
 
+
+
     /*
     Problem 3
     Return the player with the lowest ranking (largest key).
@@ -60,10 +63,10 @@ Return the player with the lowest ranking (largest key).
     public static String getLowestPlayer(TreeMap<Integer, String> map) {
 
         // TODO: Implement this method
-
-        return null;
+        return map.get(map.lastKey());
     }
 
+
     /*
     Problem 4
     Remove a player based on their rank.
@@ -75,9 +78,11 @@ public static String getLowestPlayer(TreeMap<Integer, String> map) {
     public static void removePlayer(TreeMap<Integer, String> map, int rank) {
 
         // TODO: Implement this method
-
+        map.remove(rank);
     }
 
+
+
     /*
     Problem 5
     Return the next higher rank after the given rank.
@@ -89,7 +94,8 @@ public static void removePlayer(TreeMap<Integer, String> map, int rank) {
     public static Integer getNextRank(TreeMap<Integer, String> map, int rank) {
 
         // TODO: Implement this method
-
-        return null;
+        return map.higherKey(rank);
     }
+
+
 }
diff --git a/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java b/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java
index dac03cf..7daa68c 100644
--- a/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java
+++ b/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java
@@ -31,9 +31,11 @@ public static void main(String[] args) {
     public static void addToFront(ArrayDeque<Integer> deque, int value) {
 
         // TODO: Implement this method
-
+        deque.addFirst(value);
     }
 
+
+
     /*
     Problem 2
     Add a number to the BACK of the deque.
@@ -45,9 +47,11 @@ public static void addToFront(ArrayDeque<Integer> deque, int value) {
     public static void addToBack(ArrayDeque<Integer> deque, int value) {
 
         // TODO: Implement this method
-
+        deque.addLast(value);
     }
 
+
+
     /*
     Problem 3
     Remove the element at the FRONT of the deque.
@@ -59,9 +63,11 @@ public static void addToBack(ArrayDeque<Integer> deque, int value) {
     public static void removeFront(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
-
+        deque.removeFirst();
     }
 
+
+
     /*
     Problem 4
     Remove the element at the BACK of the deque.
@@ -73,9 +79,11 @@ public static void removeFront(ArrayDeque<Integer> deque) {
     public static void removeBack(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
-
+        deque.removeLast();
     }
 
+
+
     /*
     Problem 5
     Return the FIRST element in the deque without removing it.
@@ -87,10 +95,11 @@ public static void removeBack(ArrayDeque<Integer> deque) {
     public static Integer peekFront(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
-
-        return null;
+        return deque.peekFirst();
     }
 
+
+
     /*
     Problem 6
     Return the LAST element in the deque without removing it.
@@ -102,7 +111,8 @@ public static Integer peekFront(ArrayDeque<Integer> deque) {
     public static Integer peekBack(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
-
-        return null;
+        return deque.peekLast();
     }
+
+
 }
diff --git a/src/main/java/Queues/Deque/DequeProblems.java b/src/main/java/Queues/Deque/DequeProblems.java
index 7ef0c06..bff87a3 100644
--- a/src/main/java/Queues/Deque/DequeProblems.java
+++ b/src/main/java/Queues/Deque/DequeProblems.java
@@ -1,14 +1,23 @@
 package Queues.Deque;
 
 import java.util.Deque;
+import java.util.ArrayDeque;
+
 
 public class DequeProblems {
     public static void main(String[] args) {
 
         // You can test your methods here
+        Deque<Integer> deque = new ArrayDeque<>();
+
+        addFront(deque, 5);
+        addBack(deque, 10);
+
+        System.out.println(deque);
 
     }
 
+
     /*
     Problem 1
     Add a value to the FRONT of the deque.
@@ -20,9 +29,11 @@ public static void main(String[] args) {
     public static void addFront(Deque<Integer> deque, int value) {
 
         // TODO: Implement this method
+        deque.addFirst(value);
 
     }
 
+
     /*
     Problem 2
     Add a value to the BACK of the deque.
@@ -34,9 +45,11 @@ public static void addFront(Deque<Integer> deque, int value) {
     public static void addBack(Deque<Integer> deque, int value) {
 
         // TODO: Implement this method
+        deque.addLast(value);
 
     }
 
+
     /*
     Problem 3
     Remove and return the FRONT element of the deque.
@@ -48,10 +61,13 @@ public static void addBack(Deque<Integer> deque, int value) {
     public static Integer removeFront(Deque<Integer> deque) {
 
         // TODO: Implement this method
+        deque.removeFirst();
+        return deque.removeFirst();
 
-        return null;
     }
 
+
+
     /*
     Problem 4
     Remove and return the BACK element of the deque.
@@ -63,10 +79,13 @@ public static Integer removeFront(Deque<Integer> deque) {
     public static Integer removeBack(Deque<Integer> deque) {
 
         // TODO: Implement this method
+        deque.removeLast();
+        return deque.removeLast();
 
-        return null;
     }
 
+
+
     /*
     Problem 5
     Return the FRONT element without removing it.
@@ -78,10 +97,12 @@ public static Integer removeBack(Deque<Integer> deque) {
     public static Integer peekFront(Deque<Integer> deque) {
 
         // TODO: Implement this method
+        return deque.peekFirst();
 
-        return null;
     }
 
+
+
     /*
     Problem 6
     Return the BACK element without removing it.
@@ -93,8 +114,10 @@ public static Integer peekFront(Deque<Integer> deque) {
     public static Integer peekBack(Deque<Integer> deque) {
 
         // TODO: Implement this method
+        return deque.peekLast();
 
-        return null;
     }
 
+
 }
+
diff --git a/src/main/java/Sets/HashSet/HashSetProblems.java b/src/main/java/Sets/HashSet/HashSetProblems.java
index a36c570..6fad1ce 100644
--- a/src/main/java/Sets/HashSet/HashSetProblems.java
+++ b/src/main/java/Sets/HashSet/HashSetProblems.java
@@ -2,14 +2,22 @@
 
 import java.util.List;
 import java.util.Set;
+import java.util.HashSet;
 
 public class HashSetProblems {
     public static void main(String[] args) {
 
         // You can test your methods here
+        Set<String> set = new HashSet<>();
+
+        addElement(set, "apple");
+
+        System.out.println(set); // Output: [apple]
 
     }
 
+
+
     /*
     Problem 1
     Add an element to the set.
@@ -21,9 +29,11 @@ public static void main(String[] args) {
     public static void addElement(Set<String> set, String value) {
 
         // TODO: Implement this method
-
+        set.add(value);
     }
 
+
+
     /*
     Problem 2
     Check if the set contains a value.
@@ -35,10 +45,12 @@ public static void addElement(Set<String> set, String value) {
     public static boolean containsValue(Set<String> set, String value) {
 
         // TODO: Implement this method
+        return set.contains(value);
 
-        return false;
     }
 
+
+
     /*
     Problem 3
     Remove a value from the set.
@@ -50,9 +62,12 @@ public static boolean containsValue(Set<String> set, String value) {
     public static void removeValue(Set<String> set, String value) {
 
         // TODO: Implement this method
+        set.remove(value);
 
     }
 
+
+
     /*
     Problem 4
     Return the number of unique elements in the set.
@@ -64,10 +79,12 @@ public static void removeValue(Set<String> set, String value) {
     public static int getUniqueCount(Set<String> set) {
 
         // TODO: Implement this method
+        return set.size();
 
-        return 0;
     }
 
+
+
     /*
     Problem 5
     Given a list of integers, return a HashSet containing only the unique values.
@@ -79,7 +96,9 @@ public static int getUniqueCount(Set<String> set) {
     public static Set<Integer> getUniqueValues(List<Integer> numbers) {
 
         // TODO: Implement this method
-
-        return null;
+        return new HashSet<>(numbers);
     }
+
+
+
 }