diff --git a/src/main/java/Collections/Practice/CollectionBasics.java b/src/main/java/Collections/Practice/CollectionBasics.java
index e45cb49..61dca34 100644
--- a/src/main/java/Collections/Practice/CollectionBasics.java
+++ b/src/main/java/Collections/Practice/CollectionBasics.java
@@ -2,6 +2,8 @@
 
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashSet;
+import java.util.Set;
 
 public class CollectionBasics {
     public static void main(String[] args) {
@@ -30,14 +32,13 @@ public static int sum(Collection<Integer> numbers) {
 
         int total = 0;
 
-        // TODO:
-        // Loop through the collection
-        // Add each number to total
+        for (Integer num : numbers) {
+            total += num;
+        }
 
         return total;
     }
 
-
     /*
      PROBLEM 2
      Count how many numbers are even
@@ -49,6 +50,11 @@ public static int countEven(Collection<Integer> numbers) {
         // TODO:
         // Loop through the collection
         // If the number is even, increase count
+        for (Integer num : numbers){
+            if(num % 2==0){
+                count++;
+            }
+        }
 
         return count;
     }
@@ -66,6 +72,10 @@ public static int findMax(Collection<Integer> numbers) {
         // Loop through numbers
         // Update max if current number is larger
 
+        for (Integer num : numbers){
+            max = Math.max(max, num);
+        }
+
         return max;
     }
 
@@ -81,7 +91,11 @@ public static boolean hasDuplicates(Collection<Integer> numbers) {
         // Hint:
         // Compare the size of a collection with the size of a Set
 
-        return false;
+        Set<Integer> set = new HashSet<>(numbers);
+
+
+
+        return set.size() == numbers.size();
     }
 
 
@@ -96,6 +110,11 @@ public static int countOccurrences(Collection<Integer> numbers, int target) {
         // TODO:
         // Loop through numbers
         // If number equals target, increase count
+        for(int i=0; i < numbers.size(); i++){
+            if(numbers.contains(target)){
+                count++;
+            }
+        }
 
         return count;
     }
diff --git a/src/main/java/Collections/Practice/CommonMethodsDemo.java b/src/main/java/Collections/Practice/CommonMethodsDemo.java
index b2dd6f9..8af821f 100644
--- a/src/main/java/Collections/Practice/CommonMethodsDemo.java
+++ b/src/main/java/Collections/Practice/CommonMethodsDemo.java
@@ -131,24 +131,33 @@ public static void main(String[] args) {
          Add the following values:
          10, 20, 30, 40, 50
         */
+        Collection<Integer> numbers = new ArrayList<>();
+        numbers.add(10);
+        numbers.add(20);
+        numbers.add(30);
+        numbers.add(40);
+        numbers.add(50);
 
 
         /*
          TODO 2:
          Print the size of the numbers collection
         */
+        System.out.println(numbers.size());
 
 
         /*
          TODO 3:
          Check if the collection contains 30
         */
+        System.out.println("Does collection contains 30? " + numbers.contains(30));
 
 
         /*
          TODO 4:
          Remove the number 20
         */
+        numbers.remove(30);
 
 
         /*
@@ -156,6 +165,10 @@ public static void main(String[] args) {
          Loop through the numbers collection
          and print each value
         */
+        for(Integer num : numbers){
+            System.out.println(num);
+        }
+
 
 
         /*
diff --git a/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java b/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
index 6c2f4e1..a6699a6 100644
--- a/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
+++ b/src/main/java/CollectionsHackerrank/CollectionsHackerrankProblems.java
@@ -1,8 +1,6 @@
 package CollectionsHackerrank;
 
-import java.util.List;
-import java.util.Map;
-import java.util.Queue;
+import java.util.*;
 
 public class CollectionsHackerrankProblems {
     public class CollectionsHackerrankPractice {
@@ -24,8 +22,10 @@ public static void main(String[] args) {
         public static List<Integer> removeDuplicates(List<Integer> numbers) {
 
             // TODO: Implement this method
+            HashSet<Integer> set = new HashSet<>(numbers);
 
-            return null;
+
+            return new ArrayList<>(set);
         }
 
         /*
@@ -39,8 +39,16 @@ public static List<Integer> removeDuplicates(List<Integer> numbers) {
         public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Map<Integer, Integer> map = new HashMap<>();
+            for (Integer number : numbers) {
+                map.put(number, map.getOrDefault(number, 0) + 1);
+            }
 
-            return null;
+
+
+
+
+            return map;
         }
 
         /*
@@ -54,6 +62,25 @@ public static Map<Integer, Integer> countFrequency(List<Integer> numbers) {
         public static Integer firstUnique(List<Integer> numbers) {
 
             // TODO: Implement this method
+            Map<Integer, Integer> map = new HashMap<>();
+            for (Integer number : numbers) {
+                map.put(number, map.getOrDefault(number, 0) + 1);
+
+            }
+            // next, return the first key that value = 1
+            // num = numbers list
+            // 4 insert key check value, no.
+            // 5 Insert key check value, yes.
+            for (Integer num : numbers){
+                if(map.get(num) == 1){
+                    return num;
+
+                }
+
+
+            }
+
+
 
             return null;
         }
@@ -71,6 +98,21 @@ public static Integer firstUnique(List<Integer> numbers) {
         public static boolean twoSum(List<Integer> numbers, int target) {
 
             // TODO: Implement this method
+            HashSet<Integer> set = new HashSet<>();
+
+            int complement = 0;
+
+            for (Integer num : numbers) {
+                complement = target - num;
+
+                if (set.contains(complement)) {
+                    return true;
+                }
+
+                set.add(num);
+
+            }
+
 
             return false;
         }
@@ -86,8 +128,10 @@ public static boolean twoSum(List<Integer> numbers, int target) {
         public static int countUniqueWords(List<String> words) {
 
             // TODO: Implement this method
+            HashSet<String> set = new HashSet<>(words);
 
-            return 0;
+
+            return set.size();
         }
 
         /*
@@ -101,8 +145,16 @@ public static int countUniqueWords(List<String> words) {
         public static Queue<Integer> reverseQueue(Queue<Integer> queue) {
 
             // TODO: Implement this method
-
-            return null;
+            Stack<Integer> stack = new Stack<>();
+            Queue<Integer> reverse = new ArrayDeque<>();
+              while (!(queue.isEmpty())) {
+                  stack.push(queue.poll());
+
+              }
+              while (!(stack.isEmpty())){
+                  reverse.add(stack.pop());
+              }
+            return reverse;
         }
 
         /*
@@ -118,9 +170,23 @@ 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 (int i = 0; i < expression.length(); i++) {
+                char ch = expression.charAt(i);
+
+                if (ch == '(') {
+                    stack.push(ch);
+                }
+                else if (ch == ')') {
+                    if (stack.isEmpty()) {
+                        return false;
+                    }
+                    stack.pop();
+                }
+            }
+
+            return stack.isEmpty();
         }
 
         /*
@@ -134,6 +200,21 @@ public static boolean isBalanced(String expression) {
         public static Integer mostFrequent(List<Integer> numbers) {
 
             // TODO: Implement this method
+            int max = 0;
+            HashMap<Integer, Integer> map = new HashMap<>();
+            for(Integer num : numbers){
+                map.put(num, map.getOrDefault(num, 0)+1);
+                max = Math.max(max, map.get(num));
+            }
+
+            for(Integer number: numbers){
+
+                if (max == map.get(number)){
+                    return number;
+                }
+            }
+
+
 
             return null;
         }
@@ -154,8 +235,21 @@ public static Integer mostFrequent(List<Integer> numbers) {
         public static Map<Integer, List<String>> groupByLength(List<String> words) {
 
             // TODO: Implement this method
+            HashMap<Integer, List<String>> map = new HashMap<>();
+            for(String word : words){
+                Integer length = word.length();
 
-            return null;
+                if(!(map.containsKey(length))){
+                    map.put(length, new ArrayList<>());
+                }
+
+                map.get(length).add(word);
+
+
+            }
+
+
+            return map;
         }
 
         /*
@@ -171,8 +265,21 @@ 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;
+            for (int i = 0; i < k; i++) {
+                windowSum += numbers.get(i);
+            }
+
+            int maxSum = windowSum;
+
+            // 2) slide the window
+            for (int right = k; right < numbers.size(); right++) {
+                int left = right - k;                 // index leaving the window
+                windowSum = windowSum - numbers.get(left) + numbers.get(right);
+                maxSum = Math.max(maxSum, windowSum);
+            }
 
-            return 0;
+            return maxSum;
         }
     }
 }
diff --git a/src/main/java/Hierachy/Hierarchy.java b/src/main/java/Hierachy/Hierarchy.java
index b79931f..6ed09ce 100644
--- a/src/main/java/Hierachy/Hierarchy.java
+++ b/src/main/java/Hierachy/Hierarchy.java
@@ -5,6 +5,7 @@
 public class Hierarchy {
     public static void main(String[] args) {
 
+
         // LIST EXAMPLE
         List<String> list = new ArrayList<>();
         list.add("Apple");
diff --git a/src/main/java/Iterable/Examples/ForEachLoopDemo.java b/src/main/java/Iterable/Examples/ForEachLoopDemo.java
index a6d2198..eeee705 100644
--- a/src/main/java/Iterable/Examples/ForEachLoopDemo.java
+++ b/src/main/java/Iterable/Examples/ForEachLoopDemo.java
@@ -18,20 +18,32 @@ public static void main(String[] args) {
         // TODO:
         // Use a for-each loop to print each student name
 
+        for(String name : students){
+            System.out.println(name);
+        }
+
 
         System.out.println("\nPrinting students in uppercase:");
 
         // TODO:
         // Use a for-each loop to print each name in uppercase
+        for(String name : students){
+            System.out.println(name.toUpperCase());
+        }
 
 
         System.out.println("\nCount the number of students:");
 
         int count = 0;
+        for(int i=0; i < students.size(); i++){
+           count++;
+        }
+
 
         // TODO:
         // Use a for-each loop to count how many students are in the list
 
+
         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..e5d4cbf 100644
--- a/src/main/java/Iterable/Examples/IteratorDemo.java
+++ b/src/main/java/Iterable/Examples/IteratorDemo.java
@@ -27,6 +27,10 @@ public static void main(String[] args) {
         // Use iterator.hasNext() and iterator.next()
         // Print each number
 
+        while (iterator.hasNext())
+        {
+            System.out.println(iterator.next());
+        }
 
         System.out.println("\nRemoving odd numbers using Iterator");
 
@@ -36,6 +40,13 @@ public static void main(String[] args) {
         // Use iterator to remove odd numbers
         // Remember: use iterator.remove()
 
+        while (iterator.hasNext())
+        {
+            if(! (iterator.next() % 2 == 0)){
+                iterator.remove();
+            }
+        }
+
 
         System.out.println("\nUpdated list:");
         System.out.println(numbers);
diff --git a/src/main/java/Iterable/Practice/IterableWarmups.java b/src/main/java/Iterable/Practice/IterableWarmups.java
index 9e9de94..421d19e 100644
--- a/src/main/java/Iterable/Practice/IterableWarmups.java
+++ b/src/main/java/Iterable/Practice/IterableWarmups.java
@@ -15,11 +15,12 @@ public static void main(String[] args) {
         numbers.add(8);
 
         System.out.println("Sum: " + sum(numbers));
-        System.out.println("Even count: " + countEven(numbers));
-        System.out.println("Max value: " + findMax(numbers));
+       System.out.println("Even count: " + countEven(numbers));
+       System.out.println("Max value: " + findMax(numbers));
     }
 
 
+
     /*
     PROBLEM 1
     Return the sum of all numbers in the iterable
@@ -31,6 +32,10 @@ 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;
     }
 
@@ -46,6 +51,12 @@ 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;
     }
@@ -63,6 +74,11 @@ public static int findMax(Iterable<Integer> numbers) {
         // Loop through numbers
         // Update max if current number is larger
 
+        for(Integer num : numbers){
+            max = Math.max(max, num);
+        }
+
+
         return max;
     }
 
diff --git a/src/main/java/Lists/ArrayLists/ArrayListProblems.java b/src/main/java/Lists/ArrayLists/ArrayListProblems.java
index baf4dfa..2921c6b 100644
--- a/src/main/java/Lists/ArrayLists/ArrayListProblems.java
+++ b/src/main/java/Lists/ArrayLists/ArrayListProblems.java
@@ -34,8 +34,14 @@ public static void main(String[] args) {
     public static int sum(List<Integer> nums) {
 
         // TODO: Implement this method
+       int sum = 0;
+        for(Integer num : nums){
 
-        return 0;
+           sum += num;
+
+        }
+
+        return sum;
     }
 
     /*
@@ -49,8 +55,15 @@ public static int sum(List<Integer> nums) {
     public static int countEvens(List<Integer> nums) {
 
         // TODO: Implement this method
+        int counter = 0;
+        for(Integer num : nums){
+            if (num % 2 ==0 ){
+                counter++;
+            }
+        }
 
-        return 0;
+
+        return counter;
     }
 
     /*
@@ -66,9 +79,20 @@ public static int countEvens(List<Integer> nums) {
     */
     public static boolean hasDuplicate(List<Integer> nums) {
 
-        // TODO: Implement this method
+        ArrayList<Integer> findDup = new ArrayList<>();
+
+        for (Integer num : nums) {
+
+            if (findDup.contains(num)) {
+                return true;
+            }
+
+            findDup.add(num);
+        }
 
         return false;
+
+
     }
 
     /*
@@ -82,8 +106,13 @@ public static boolean hasDuplicate(List<Integer> nums) {
     public static int findMax(List<Integer> nums) {
 
         // TODO: Implement this method
+        int max = nums.get(0);
 
-        return 0;
+        for (Integer num : nums){
+            max = Math.max(max, num);
+        }
+
+        return max;
     }
 
     /*
@@ -98,8 +127,18 @@ public static int findMax(List<Integer> nums) {
     */
     public static List<Integer> reverse(List<Integer> nums) {
 
+        ArrayList<Integer> reverseList = new ArrayList<>(nums.size()-1);
+        int counter = 0;
+
         // TODO: Implement this method
 
-        return null;
+        for (int i = nums.size()-1; i >= 0; i--){
+                reverseList.add(counter, nums.get(i));
+                counter++;
+
+        }
+
+
+        return reverseList;
     }
 }
diff --git a/src/main/java/Lists/LinkedLists/LinkedListProblems.java b/src/main/java/Lists/LinkedLists/LinkedListProblems.java
index 178a2ba..94de027 100644
--- a/src/main/java/Lists/LinkedLists/LinkedListProblems.java
+++ b/src/main/java/Lists/LinkedLists/LinkedListProblems.java
@@ -38,6 +38,7 @@ public static void main(String[] args) {
     public static void addToFront(LinkedList<Integer> list, int value) {
 
         // TODO: Implement this method
+        list.addFirst(value);
 
     }
 
@@ -52,6 +53,7 @@ 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);
 
     }
 
@@ -67,6 +69,7 @@ public static void removeFirstElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
 
+        list.removeFirst();
     }
 
     /*
@@ -80,6 +83,7 @@ public static void removeFirstElement(LinkedList<Integer> list) {
     public static void removeLastElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
+        list.removeLast();
 
     }
 
@@ -94,8 +98,9 @@ public static void removeLastElement(LinkedList<Integer> list) {
     public static int getFirstElement(LinkedList<Integer> list) {
 
         // TODO: Implement this method
+       return list.getFirst();
+
 
-        return 0;
     }
 
     /*
@@ -110,6 +115,7 @@ 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..6a0dc54 100644
--- a/src/main/java/Maps/HashMap/HashMapProblems.java
+++ b/src/main/java/Maps/HashMap/HashMapProblems.java
@@ -22,6 +22,8 @@ public static void main(String[] args) {
 
         removeItem(inventory, "Oranges");
         System.out.println("After Removal: " + inventory);
+
+
     }
 
     /*
@@ -30,11 +32,12 @@ public static void main(String[] args) {
 
     Example
     Input: ("Apples", 10)
-    Output: {"Apples"=10}
+    Output: {"Apples" = 10}
     */
     public static void addItem(Map<String, Integer> map, String item, int quantity) {
 
         // TODO: Implement this method
+        map.put(item, quantity);
 
     }
 
@@ -50,7 +53,8 @@ public static int getQuantity(Map<String, Integer> map, String item) {
 
         // TODO: Implement this method
 
-        return 0;
+
+        return map.get(item);
     }
 
     /*
@@ -64,6 +68,7 @@ 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);
 
     }
 
@@ -78,6 +83,7 @@ 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);
 
     }
 
@@ -92,7 +98,19 @@ 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> frequent = new HashMap<>();
+
+
+
+        for(Integer num : numbers){
+            frequent.put(num,frequent.getOrDefault(num, 0)+1);
+        }
+
+
+
+
+
 
-        return null;
+        return frequent;
     }
 }
diff --git a/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java b/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
index e8bbdc2..587c370 100644
--- a/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
+++ b/src/main/java/Maps/LinkedHashMap/LinkedHashMapProblems.java
@@ -1,8 +1,6 @@
 package Maps.LinkedHashMap;
 
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 public class LinkedHashMapProblems {
     public static void main(String[] args) {
@@ -33,6 +31,7 @@ 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);
 
     }
 
@@ -47,6 +46,7 @@ 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);
 
     }
 
@@ -61,6 +61,9 @@ 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);
+
+
 
     }
 
@@ -75,8 +78,15 @@ public static void removeStudent(Map<String, Integer> map, String name) {
     public static String getFirstInserted(Map<String, Integer> map) {
 
         // TODO: Implement this method
+        Set<String> keys = map.keySet();
+
+
+        Iterator<String> iterator = keys.iterator();
+        return iterator.next();
+
+
+
 
-        return null;
     }
 
     /*
@@ -91,7 +101,17 @@ public static String getFirstInserted(Map<String, Integer> map) {
     public static Map<String, Integer> wordFrequency(List<String> words) {
 
         // TODO: Implement this method
+        Map<String, Integer> frequent = new LinkedHashMap<>();
+
+
+
+        for(String items : words){
+            frequent.put(items,frequent.getOrDefault(items, 0)+1);
+        }
+
+
+
 
-        return null;
+        return frequent;
     }
 }
diff --git a/src/main/java/Maps/TreeMap/TreeMapProblems.java b/src/main/java/Maps/TreeMap/TreeMapProblems.java
index b101d2e..2e53f25 100644
--- a/src/main/java/Maps/TreeMap/TreeMapProblems.java
+++ b/src/main/java/Maps/TreeMap/TreeMapProblems.java
@@ -1,5 +1,7 @@
 package Maps.TreeMap;
 
+import java.util.Iterator;
+import java.util.Set;
 import java.util.TreeMap;
 
 public class TreeMapProblems {
@@ -31,6 +33,7 @@ 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);
 
     }
 
@@ -46,7 +49,8 @@ public static String getTopPlayer(TreeMap<Integer, String> map) {
 
         // TODO: Implement this method
 
-        return null;
+
+        return map.get(1);
     }
 
     /*
@@ -61,7 +65,7 @@ public static String getLowestPlayer(TreeMap<Integer, String> map) {
 
         // TODO: Implement this method
 
-        return null;
+        return map.get(map.size());
     }
 
     /*
@@ -75,6 +79,7 @@ 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);
 
     }
 
@@ -86,10 +91,12 @@ public static void removePlayer(TreeMap<Integer, String> map, int rank) {
     Input: rank=2, map={1="A",2="B",3="C"}
     Output: 3
     */
+
     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..33ee302 100644
--- a/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java
+++ b/src/main/java/Queues/ArrayDeque/ArrayDequeProblems.java
@@ -31,6 +31,7 @@ public static void main(String[] args) {
     public static void addToFront(ArrayDeque<Integer> deque, int value) {
 
         // TODO: Implement this method
+        deque.addFirst(value);
 
     }
 
@@ -45,6 +46,7 @@ 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);
 
     }
 
@@ -59,6 +61,7 @@ public static void addToBack(ArrayDeque<Integer> deque, int value) {
     public static void removeFront(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
+        deque.removeFirst();
 
     }
 
@@ -73,6 +76,7 @@ public static void removeFront(ArrayDeque<Integer> deque) {
     public static void removeBack(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
+        deque.removeLast();
 
     }
 
@@ -88,7 +92,7 @@ public static Integer peekFront(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.getFirst();
     }
 
     /*
@@ -103,6 +107,6 @@ public static Integer peekBack(ArrayDeque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.getLast();
     }
 }
diff --git a/src/main/java/Queues/Deque/DequeProblems.java b/src/main/java/Queues/Deque/DequeProblems.java
index 7ef0c06..e7017f0 100644
--- a/src/main/java/Queues/Deque/DequeProblems.java
+++ b/src/main/java/Queues/Deque/DequeProblems.java
@@ -7,6 +7,7 @@ public static void main(String[] args) {
 
         // You can test your methods here
 
+
     }
 
     /*
@@ -20,6 +21,7 @@ public static void main(String[] args) {
     public static void addFront(Deque<Integer> deque, int value) {
 
         // TODO: Implement this method
+        deque.addFirst(value);
 
     }
 
@@ -34,6 +36,7 @@ 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);
 
     }
 
@@ -49,7 +52,7 @@ public static Integer removeFront(Deque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.removeFirst();
     }
 
     /*
@@ -64,7 +67,7 @@ public static Integer removeBack(Deque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.removeLast();
     }
 
     /*
@@ -79,7 +82,7 @@ public static Integer peekFront(Deque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.getFirst();
     }
 
     /*
@@ -94,7 +97,7 @@ public static Integer peekBack(Deque<Integer> deque) {
 
         // TODO: Implement this method
 
-        return null;
+        return deque.getLast();
     }
 
 }
diff --git a/src/main/java/Sets/HashSet/HashSetProblems.java b/src/main/java/Sets/HashSet/HashSetProblems.java
index a36c570..d50efd7 100644
--- a/src/main/java/Sets/HashSet/HashSetProblems.java
+++ b/src/main/java/Sets/HashSet/HashSetProblems.java
@@ -1,5 +1,6 @@
 package Sets.HashSet;
 
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -21,6 +22,7 @@ public static void main(String[] args) {
     public static void addElement(Set<String> set, String value) {
 
         // TODO: Implement this method
+        set.add(value);
 
     }
 
@@ -36,7 +38,7 @@ public static boolean containsValue(Set<String> set, String value) {
 
         // TODO: Implement this method
 
-        return false;
+        return set.contains(value);
     }
 
     /*
@@ -50,6 +52,7 @@ 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);
 
     }
 
@@ -65,7 +68,8 @@ public static int getUniqueCount(Set<String> set) {
 
         // TODO: Implement this method
 
-        return 0;
+
+        return set.size();
     }
 
     /*
@@ -80,6 +84,6 @@ public static Set<Integer> getUniqueValues(List<Integer> numbers) {
 
         // TODO: Implement this method
 
-        return null;
+        return new HashSet<>(numbers);
     }
 }