diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..c995aa5
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "java.debug.settings.onBuildFailureProceed": true
+}
\ No newline at end of file
diff --git a/src/ListNode.java b/src/ListNode.java
index ff02b96..2a7d4ff 100644
--- a/src/ListNode.java
+++ b/src/ListNode.java
@@ -10,4 +10,4 @@ public ListNode(T data, ListNode<T> next) {
     public ListNode(T data) {
         this(data, null);
     }
-}
+}
\ No newline at end of file
diff --git a/src/Practice.java b/src/Practice.java
index 01da8d0..292eabe 100644
--- a/src/Practice.java
+++ b/src/Practice.java
@@ -1,3 +1,5 @@
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
@@ -11,7 +13,14 @@ public class Practice {
      * @return the sum of the odd numbers in the array
      */
     public static int oddSum(int[] nums) {
-        return 0;
+        int sum = 0;
+        if (nums == null)
+            return 0;
+        for (int num : nums) {
+            if (num % 2 != 0)
+                sum += num;
+        }
+        return sum;
     }
 
     /**
@@ -23,10 +32,31 @@ public static int oddSum(int[] nums) {
      * @param words a set of words
      * @return the shortest word in the set with a lexicographic tiebreaker
      * @throws IllegalArgumentException if words is empty
-     * @throws NullPointerException if words is null
+     * @throws NullPointerException     if words is null
      */
     public static String shortestWord(Set<String> words) {
-        return null;
+        if (words == null) {
+            throw new NullPointerException("Word is null");
+        }
+        if (words.isEmpty()) {
+            throw new IllegalArgumentException("Word is empty");
+        }
+
+        String shortest = null;
+
+        for (String word : words) {
+            if (shortest == null)
+                shortest = word;
+            if (word.length() < shortest.length()) {
+                shortest = word;
+            }
+            if (word.length() == shortest.length()) {
+                if (word.compareTo(shortest) < 0) {
+                    shortest = word;
+                }
+            }
+        }
+        return shortest;
     }
 
     /**
@@ -39,9 +69,23 @@ public static String shortestWord(Set<String> words) {
      * @throws NullPointerException if ages is null
      */
     public static Set<String> adults(Map<String, Integer> ages) {
-        return null;
-    }
+        if (ages == null) {
+            throw new NullPointerException();
+        }
+
+        Set<String> result = new HashSet<>();
 
+        for (String name : ages.keySet()){
+            int age = ages.get(name);
+
+            if (age >= 18){
+                result.add(name);
+            }
+        }
+
+        return result;
+    }
+    
     /**
      * Returns the biggest number in a linked list.
      * 
@@ -50,26 +94,46 @@ public static Set<String> adults(Map<String, Integer> ages) {
      * @throws IllegalArgumentException if head is null
      */
     public static int biggestNumber(ListNode<Integer> head) {
-        return 0;
+         if (head == null) throw new IllegalArgumentException();
+        int biggestNumber = head.data;
+        ListNode<Integer> current = head;
+        while (current != null) {
+            if (current.data > biggestNumber) biggestNumber = current.data;
+            current = current.next;
+        }
+        return biggestNumber;
     }
 
+
     /**
-     * Returns a frequency map counting how frequently items appear in a linked list.
+     * Returns a frequency map counting how frequently items appear in a linked
+     * list.
      * 
      * Example:
-     *   Input: a -> x -> a -> a -> x -> y
-     *   Output: {a:3, x:2, y: 1}
+     * Input: a -> x -> a -> a -> x -> y
+     * Output: {a:3, x:2, y: 1}
      * 
      * Returns an empty map if head is null
      * 
-     * @param <T> the type of data held by the list
+     * @param <T>  the type of data held by the list
      * @param head the head of the list
      * @return a frequency map of values in the list
      */
     public static <T> Map<T, Integer> frequencies(ListNode<T> head) {
-        return null;
-    }
+        Map<T, Integer> results = new HashMap<>();
+        if (head == null) return results;
+        ListNode<T> current = head;
+        while (current != null) {
+            if (results.containsKey(current.data)) {
+                results.put(current.data, results.get(current.data) + 1);
+            } else {
+                results.put(current.data, 1);
+            }
+            current = current.next;
+        }
 
+        return results;
+    }
 
     /**
      * Returns the number of levels in the tree.
@@ -80,41 +144,53 @@ public static <T> Map<T, Integer> frequencies(ListNode<T> head) {
      * @return the number of levels in the tree
      */
     public static int levelCount(BinaryTreeNode<?> root) {
-        return 0;
-    }
+        if (root == null){
+            return 0;
+        }
 
+        return 1 + Math.max(levelCount(root.left),
+        levelCount(root.right));
+    }
 
     /**
      * Returns the sum at a specified level in a binary tree.
      * 
      * For example, if the given level was 3:
-     *       5
-     *     /   \
-     *    8     4
-     *   / \   / 
-     *  7  9  2
-     *    /
-     *   1
+     * 5
+     * / \
+     * 8 4
+     * / \ /
+     * 7 9 2
+     * /
+     * 1
      * 
      * Nodes at level 3: 7, 9, and 2
-     * Sum of nodes at level 3: 18 
+     * Sum of nodes at level 3: 18
      * 
      * The root is considered to be at level 1.
      * 
      * Returns 0 if the tree is empty or if the level is not present in the tree.
      * 
-     * @param root the root of the binary tree
+     * @param root  the root of the binary tree
      * @param level the level to sum
      * @return the sum of the nodes at the given level
      */
     public static int sumAtLevel(BinaryTreeNode<Integer> root, int level) {
-        return 0;
-    }
+        if (root == null){
+            return 0;
+        }
+        if (level == 1){
+            return root.data;
+        }
 
+        return sumAtLevel(root.left, level -1) +
+        sumAtLevel(root.right, level -1);
+       
+    }
 
     /**
      * Returns true if the sum of the values in a given tree is equal to the sum
-     * of the values in the given list. 
+     * of the values in the given list.
      * 
      * An empty tree or list is considered to have a sum of 0.
      * 
@@ -123,11 +199,29 @@ public static int sumAtLevel(BinaryTreeNode<Integer> root, int level) {
      * @return true if the sums are equal, false otherwise
      */
     public static boolean sumMatch(BinaryTreeNode<Integer> root, ListNode<Integer> head) {
-        return false;
+    int treeSum = sumTree(root);
+    int listSum = sumList(head);
+    return treeSum == listSum;
+    }
+
+    private static int sumTree(BinaryTreeNode<Integer> root) {
+        if (root == null) return 0;
+        return root.data + sumTree(root.left) + sumTree(root.right);
     }
 
+    private static int sumList(ListNode<Integer> head){
+        int sum = 0;
+        ListNode<Integer> current = head;
+        while (current != null) {
+            sum += current.data;
+            current = current.next;
+        }
+        return sum;
+    }
+    
     /**
-     * Returns the sum of all the vertices in a graph that are reachable from a given
+     * Returns the sum of all the vertices in a graph that are reachable from a
+     * given
      * starting vertex.
      * 
      * Returns 0 if the starting vertex is null.
@@ -136,7 +230,28 @@ public static boolean sumMatch(BinaryTreeNode<Integer> root, ListNode<Integer> h
      * @return the sum of all the vertices
      */
     public static int graphSum(Vertex<Integer> start) {
-        return 0;
+        if(start == null){
+            return 0;
+        }
+
+        Set<Vertex<Integer>> visited = new HashSet<>();
+        return Sum(start, visited);
+
+    }
+
+    private static int Sum(Vertex<Integer> v, Set<Vertex<Integer>> visited){
+        if (visited.contains(v)){
+            return 0;
+        }
+
+        visited.add(v);
+
+        int sum = v.data;
+
+        for (Vertex<Integer> neighbor : v.neighbors){
+            sum += Sum(neighbor, visited);
+        }
+        return sum;
     }
 
     /**
@@ -148,6 +263,29 @@ public static int graphSum(Vertex<Integer> start) {
      * @return the count of vertices with outdegree 0
      */
     public static int sinkCount(Vertex<Integer> start) {
-        return 0;
+        if (start == null){
+            return 0;
+        }
+
+        Set<Vertex<Integer>>visited = new HashSet<>();
+        return sinkCount(start, visited);
+    }
+
+    private static int sinkCount(Vertex<Integer> v, Set<Vertex<Integer>> visited) {
+        if (visited.contains(v)){
+            return 0;
+        }
+
+        visited.add(v);
+
+        int count = 0;
+        if(v.neighbors.isEmpty()){
+            count = 1;
+        }
+
+        for (Vertex<Integer> neighbor : v.neighbors){
+            count += sinkCount(neighbor, visited);
+        }
+        return count;
     }
 }
\ No newline at end of file