diff --git a/src/Practice.java b/src/Practice.java
index 01da8d0..8e6181b 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 +13,16 @@ 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 sum;
+        }
+        for (int i = 0; i < nums.length; i++) {
+            if (nums[i] % 2 != 0) {
+                sum += nums[i];
+            }
+        }
+        return sum;
     }
 
     /**
@@ -23,10 +34,35 @@ 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.isEmpty()) {
+            throw new IllegalArgumentException();
+        }
+        String shortWord = "";
+        for (String word : words) {
+            if (word == null) {
+                throw new NullPointerException();
+            }
+            if (shortWord.equals("") || word.length() < shortWord.length()) {
+                shortWord = word;
+            } else if (word.length() == shortWord.length()) {
+
+                for (int i = 0; i < word.length(); i++) {
+
+                    if (word.charAt(i) != shortWord.charAt(i)) {
+
+                        if ((int) word.charAt(i) < (int) shortWord.charAt(i)) {
+                            shortWord = word;
+                        }
+                        break;
+                    }
+                }
+            }
+        }
+
+        return shortWord;
     }
 
     /**
@@ -39,7 +75,16 @@ 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> nameSet = new HashSet<>();
+        for (String name : ages.keySet()) {
+            if (ages.get(name) >= 18) {
+                nameSet.add(name);
+            }
+        }
+        return nameSet;
     }
 
     /**
@@ -50,26 +95,55 @@ 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 biggest = Integer.MIN_VALUE;
+        ListNode<Integer> current = head;
+        while (current != null) {
+            if (current.data > biggest) {
+                biggest = current.data;
+            }
+            current = current.next;
+        }
+        return biggest;
     }
 
     /**
-     * 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> frequencyMap = new HashMap<>();
+        if (head == null) {
+            return frequencyMap;
+        }
+
+        ListNode<T> current = head;
+        while (current != null) {
+            if (frequencyMap.containsKey(current.data)) {
+                int count = frequencyMap.get(current.data);
+                count += 1;
+                frequencyMap.put(current.data, count);
+            } else {
+                frequencyMap.put(current.data, 1);
+            }
+            current = current.next;
+        }
 
+        return frequencyMap;
+    }
 
     /**
      * Returns the number of levels in the tree.
@@ -80,41 +154,69 @@ 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;
-    }
+        int levels = 0;
+        if (root == null) {
+            return levels;
+        }
+        levels++;
 
+        int maxDepth = Math.max(levelCount(root.left), levelCount(root.right));
+        levels += maxDepth;
+
+        return levels;
+    }
 
     /**
      * 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;
+        }
+
+        return sumAtLevel(root, level, 1);
     }
 
+    public static int sumAtLevel(BinaryTreeNode<Integer> root, int level, int currentLevel) {
+        int sum = 0;
+        if (root == null) {
+            return sum;
+        }
+
+        if (currentLevel == level) {
+            sum = root.data;
+        }
+
+        currentLevel++;
+        sum += sumAtLevel(root.left, level, currentLevel);
+        sum += sumAtLevel(root.right, level, currentLevel);
+
+        return sum;
+    }
 
     /**
      * 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 +225,40 @@ 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) {
+        int lSum = 0;
+        int tSum = 0;
+        if (head != null) {
+            ListNode<Integer> current = head;
+            while (current != null) {
+                lSum += current.data;
+                current = current.next;
+            }
+        }
+        if (root != null) {
+            tSum = treeSum(root);
+        }
+
+        if (lSum == tSum) {
+            return true;
+        }
         return false;
     }
 
+    public static int treeSum(BinaryTreeNode<Integer> root) {
+        int sum = 0;
+        if (root == null) {
+            return sum;
+        }
+
+        sum = root.data;
+        sum += treeSum(root.left);
+        sum += treeSum(root.right);
+        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 +267,23 @@ 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;
+        Set<Vertex<Integer>> visited = new HashSet<>();
+        return graphSum(start, visited);
+    }
+
+    public static int graphSum(Vertex<Integer> start, Set<Vertex<Integer>> visited) {
+        int sum = 0;
+        if (start == null || visited.contains(start)) {
+            return sum;
+        }
+
+        visited.add(start);
+        sum += start.data;
+        for (Vertex<Integer> neighbor : start.neighbors) {
+            sum += graphSum(neighbor, visited);
+        }
+
+        return sum;
     }
 
     /**
@@ -148,6 +295,26 @@ 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);
+    }
+
+    public static int sinkCount(Vertex<Integer> start, Set<Vertex<Integer>> visited) {
+        int total = 0;
+        if (start == null || visited.contains(start)) {
+            return 0;
+        }
+
+        visited.add(start);
+        if (start.neighbors.isEmpty()) {
+            total++;
+        }
+        for (Vertex<Integer> neighbor : start.neighbors) {
+            total += sinkCount(neighbor, visited);
+        }
+        return total;
     }
 }
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