diff --git a/src/Practice.java b/src/Practice.java
index 01da8d0..3c0335a 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 0;
+        }
+        for (int num : nums) {
+            if (num % 2 != 0){
+                sum += num;
+            }
+        }
+        return sum;
     }
 
     /**
@@ -20,13 +31,27 @@ public static int oddSum(int[] nums) {
      * If multiple words are tied for shortest, returns the one that is smallest
      * lexicographically.
      * 
-     * @param words a set of words
+     * @param words a set of word
      * @return the shortest word in the set with a lexicographic tiebreaker
      * @throws IllegalArgumentException if words is empty
      * @throws NullPointerException if words is null
      */
     public static String shortestWord(Set<String> words) {
-        return null;
+        if (words == null) {
+            throw new NullPointerException();
+        }
+        if (words.isEmpty()) {
+            throw new IllegalArgumentException();
+        }
+
+        String shortest = null;
+        for (String word : words) {
+            if (shortest == null || word.length() < shortest.length() 
+            || (word.length() == shortest.length() && word.compareTo(shortest) < 0)) {
+                shortest = word;
+            }
+        }
+        return shortest;
     }
 
     /**
@@ -39,7 +64,19 @@ 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()) {
+            Integer age = ages.get(name);
+
+            if (age >= 18) {
+                result.add(name);
+            }
+        }
+        return result;
     }
 
     /**
@@ -50,7 +87,20 @@ 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 = head.data;
+        ListNode<Integer> current = head.next;
+
+        while (current != null) {
+            if (current.data > biggest) {
+                biggest = current.data;
+            }
+            current = current.next;
+        }
+        return biggest;
     }
 
     /**
@@ -67,7 +117,22 @@ public static int biggestNumber(ListNode<Integer> head) {
      * @return a frequency map of values in the list
      */
     public static <T> Map<T, Integer> frequencies(ListNode<T> head) {
-        return null;
+        Map<T, Integer> frequency = new HashMap<>();
+        if (head == null) {
+            return frequency;
+        }
+
+        ListNode<T> current = head;
+        while (current != null) {
+            T data = current.data;
+            if (frequency.containsKey(data)) {
+                frequency.put(data, frequency.get(data) + 1);
+            } else {
+                frequency.put(data, 1);
+            }
+            current = current.next;
+        }
+        return frequency;
     }
 
 
@@ -80,7 +145,14 @@ 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;
+        }
+
+        int left = levelCount(root.left);
+        int right = levelCount(root.right);
+
+        return Math.max(left, right) + 1;
     }
 
 
@@ -108,7 +180,18 @@ public static int levelCount(BinaryTreeNode<?> root) {
      * @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;
+        }
+
+        int left = sumAtLevel(root.left, level - 1);    
+        int right = sumAtLevel(root.right, level - 1);
+
+        return left + right;
     }
 
 
@@ -123,7 +206,32 @@ 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 = 0;
+        
+        if (root != null) {
+            treeSum = root.data;
+            if (root.left != null) {
+                treeSum += sumMatchHelper(root.left);
+            }
+            if (root.right != null) {
+                treeSum += sumMatchHelper(root.right);
+            }
+        }
+
+        int listSum = 0;
+        ListNode<Integer> current = head;
+        while (current != null) {
+            listSum += current.data;
+            current = current.next;
+        }
+        return treeSum == listSum;
+    }
+
+    public static int sumMatchHelper(BinaryTreeNode<Integer> node) {
+        if (node == null) {
+            return 0;
+        }
+        return node.data + sumMatchHelper(node.left) + sumMatchHelper(node.right);
     }
 
     /**
@@ -136,7 +244,24 @@ 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 graphSumHelper(start, visited);
+    }
+
+    public static int graphSumHelper(Vertex<Integer> current, Set<Vertex<Integer>> visited) {
+        if (visited.contains(current)) {
+            return 0;
+        }
+        visited.add(current);
+
+        int sum = current.data;
+        for (Vertex<Integer> neighbor : current.neighbors) {
+            sum += graphSumHelper(neighbor, visited);
+        }
+        return sum;
     }
 
     /**
@@ -148,6 +273,29 @@ 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 sinkCountHelper(start, visited);
+    }
+
+    public static int sinkCountHelper(Vertex<Integer> current, Set<Vertex<Integer>> visited) {
+        // visited vertex
+        if (visited.contains(current)) {
+            return 0;
+        }
+        visited.add(current);
+
+        int count = 0;
+        if (current.neighbors.isEmpty()) {
+            count = 1;
+        }
+
+        for (Vertex<Integer> neighbor : current.neighbors) {
+            count += sinkCountHelper(neighbor, visited);
+        }
+        return count;
     }
 }
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