diff --git a/src/Practice.java b/src/Practice.java
index ab2d1c5..bb786fb 100644
--- a/src/Practice.java
+++ b/src/Practice.java
@@ -5,8 +5,8 @@
 
 public class Practice {
 
-  // Time Complexity:
-  // Space Complexity: 
+  // Time Complexity: O(n)
+  // Space Complexity: O(n)
   public static List<Integer> findEvens(int[] array) {
     List<Integer> evens = new ArrayList<>();
     for (int num : array) {
@@ -17,8 +17,8 @@ public static List<Integer> findEvens(int[] array) {
     return evens;
   }
 
-  // Time Complexity:
-  // Space Complexity: 
+  // Time Complexity: O(n)
+  // Space Complexity: O(1)
   public static int sumDiagonal(int[][] matrix) {
     int sum = 0;
     for (int i = 0; i < matrix.length; i++) {
@@ -28,8 +28,8 @@ public static int sumDiagonal(int[][] matrix) {
   }
   
 
-  // Time Complexity: 
-  // Space Complexity: 
+  // Time Complexity: O(n)
+  // Space Complexity: O(n)
   // Does the 'T' look confusing? Consider refreshing on generic methods
   // We'll revisit generics as a class later
   public static <T> Map<T, Integer> countFrequencies(T[] array) {
@@ -49,8 +49,8 @@ public static <T> Map<T, Integer> countFrequencies(T[] array) {
    * 
    * Once you finish, WRITE TESTS FOR IT in PracticeTest.java
    * 
-   * Time Complexity: 
-   * Space Complexity: 
+   * Time Complexity: O(n)
+   * Space Complexity: O(n)
    * 
    * @param nums An array of integers
    * @return the integer that shows up most commonly
@@ -58,7 +58,29 @@ public static <T> Map<T, Integer> countFrequencies(T[] array) {
   public static int mostCommonTimeEfficient(int[] nums) {
     // TODO: Complete this method with an implementation that runs
     // in O(n) time. n = nums.size()
-    return -1;
+    if (nums.length == 0 || nums == null) {
+      throw new IllegalArgumentException("Array is null or empty");
+    } else {
+      // will hold number at first index and initiate count
+      int number = nums[0];
+      int freqCount = 0;
+      // stores numbers and frequencies in a hashmap
+      Map<Integer, Integer> numCount = new HashMap<>();
+      // iterate through and count, update number/count if one with more apperances is found
+      for (int num: nums) {
+        int count = numCount.getOrDefault(num, 0) + 1;
+        numCount.put(num, count);
+
+        if (count > freqCount) {
+          number = num;
+          freqCount = count;
+        }  else if (count == freqCount && num > number) {
+          number = num;
+        }
+      }
+      // return most frequent number
+      return number; 
+    }
   }
 
   /**
@@ -70,8 +92,8 @@ public static int mostCommonTimeEfficient(int[] nums) {
    * 
    * Once you finish, WRITE TESTS FOR IT in PracticeTest.java
    * 
-   * Time Complexity: 
-   * Space Complexity: 
+   * Time Complexity: O(n^2)
+   * Space Complexity: O(1)
    * 
    * @param nums An array of integers
    * @return the integer that shows up most commonly
@@ -79,6 +101,29 @@ public static int mostCommonTimeEfficient(int[] nums) {
   public static int mostCommonSpaceEfficient(int[] nums) {
     // TODO: Complete this method with an implementation that runs
     // in O(1) space.
-    return -1;
+    if (nums.length == 0 || nums == null) {
+      throw new IllegalArgumentException("Array is null or empty");
+    } else if (nums.length == 1) {
+      return nums[0];
+    } else {
+      int number = 0;
+      int count = 0;
+      for (int i : nums) {
+        int currentNum = i;
+        int currentCount = 0;
+        for (int j = 0; j < nums.length; j++) {
+          if (currentNum == nums[j]) {
+            currentCount++;
+          }
+        }
+        if (currentCount > count) {
+          count = currentCount;
+          number = currentNum;
+        } else if (currentCount == count && currentNum > number) {
+          number = currentNum;
+        }
+      }
+      return number;
+    }
   }
 }
\ No newline at end of file
diff --git a/src/PracticeTest.java b/src/PracticeTest.java
index a0bdf6c..25a53e4 100644
--- a/src/PracticeTest.java
+++ b/src/PracticeTest.java
@@ -8,4 +8,78 @@ public class PracticeTest {
 
   // Hints: They are static methods, so you will use the full Practice.mostCommonTimeEfficient for method calls
   // Forgot how to do unit tests? Look back at the ramblebot tests or old slides for a refresher!
+
+  @Test
+  void testMostCommonTimeEfficient() {
+    int[] nums = {4, 4, 2, 5, 1, 7, 3};
+    int commonNum = Practice.mostCommonTimeEfficient(nums);
+    assertEquals(4, commonNum);
+  }
+
+  @Test
+  void testMostCommonSpaceEfficient() {
+    int[] nums = {3, 3, 4, 5, 1, 3, 3};
+    int commonNum = Practice.mostCommonSpaceEfficient(nums);
+    assertEquals(3, commonNum);
+  }
+
+  @Test
+  void testMostCommonSpaceEfficientOneElement() {
+    int[] nums = {3};
+    int commonNum = Practice.mostCommonSpaceEfficient(nums);
+    assertEquals(3, commonNum);
+  }
+
+  @Test
+  void testMostCommonTimeEfficientOneElement() {
+    int[] nums = {3};
+    int commonNum = Practice.mostCommonTimeEfficient(nums);
+    assertEquals(3, commonNum);
+  }
+  
+  @Test
+  void testMostCommonSpaceEfficientTie() {
+    int[] nums = {7, 7, 2, 2, 1, 4, 4, 1};
+    int commonNum = Practice.mostCommonSpaceEfficient(nums);
+    assertEquals(7, commonNum);
+  }
+
+  @Test
+  void testMostCommonTimeEfficientTie() {
+    int[] nums = {7, 7, 9, 9, 1, 8, 8, 1};
+    int commonNum = Practice.mostCommonTimeEfficient(nums);
+    assertEquals(9, commonNum);
+  }
+
+  @Test
+  void testMostCommonTimeEfficientSameElements() {
+    int[] nums = {9, 9, 9, 9};
+    int commonNum = Practice.mostCommonTimeEfficient(nums);
+    assertEquals(9, commonNum);
+  }
+
+  @Test
+  void testMostCommonSpaceEfficientSameElements() {
+    int[] nums = {9, 9, 9, 9};
+    int commonNum = Practice.mostCommonSpaceEfficient(nums);
+    assertEquals(9, commonNum);
+  }
+
+  @Test
+  void testMostCommonTimeEfficientNoElements() {
+    int[] nums = {};
+    // Uses a lambda expression to wrap the method call to be tested
+    assertThrows(IllegalArgumentException.class, () -> {
+      Practice.mostCommonTimeEfficient(nums);
+    });
+  }
+
+  @Test
+  void testMostCommonSpaceEfficientNoElements() {
+    int[] nums = {};
+    // Uses a lambda expression to wrap the method call to be tested
+    assertThrows(IllegalArgumentException.class, () -> {
+      Practice.mostCommonSpaceEfficient(nums);
+    });
+  }
 }