diff --git a/lib/exercises.js b/lib/exercises.js
index 648394e..13fd8cc 100644
--- a/lib/exercises.js
+++ b/lib/exercises.js
@@ -1,17 +1,24 @@
 // This method will return an array of arrays.
 // Each subarray will have strings which are anagrams of each other
-// Time Complexity: ?
-// Space Complexity: ?
+// Time Complexity: O(n log n), where n is the combined length of the input strings (since the strings are being sorted)
+// Space Complexity: O(n), where n is the length of the input array.
 function grouped_anagrams(strings) {
-  throw new Error("Method hasn't been implemented yet!");
-}
+  const indexHash = {};
+  strings.forEach ((string) => {
+    const tempString = string.split('').sort().join('');
+    if (!indexHash[tempString]) {
+      indexHash[tempString] = [string];
+    } else {
+      indexHash[tempString].push(string);
+    }
+  }) 
+
+  const returnArray = []
 
-// This method will return the k most common elements
-// in the case of a tie it will select the first occuring element.
-// Time Complexity: ?
-// Space Complexity: ?
-function top_k_frequent_elements(list, k) {
-  throw new Error("Method hasn't been implemented yet!");
+  for (let key in indexHash) {
+    returnArray.push(indexHash[key])
+  }
+return returnArray;
 }
 
 
@@ -20,10 +27,56 @@ function top_k_frequent_elements(list, k) {
 //   Each element can either be a ".", or a digit 1-9
 //   The same digit cannot appear twice or more in the same 
 //   row, column or 3x3 subgrid
-// Time Complexity: ?
-// Space Complexity: ?
+// Time Complexity: O(n), where n is the number of elements in the sudoku table
+// Space Complexity: O(n), where n is the number of elements in the sudoku table
 function valid_sudoku(table) {
-  throw new Error("Method hasn't been implemented yet!");
+  // check rows
+
+  for (let row = 0; row < table.length; row++) {
+    const rowHash = {};
+    for (let i = 0; i < table[row].length; i++) {
+      let char = table[row][i]
+      if (char !== ".") {
+        if (rowHash[char]) {
+          return false;
+        } 
+        rowHash[char] = 1;
+      }
+    }
+  }
+
+  for (let i = 0; i < table[0].length; i++) {
+    const colHash = {};
+    for (let col = 0; col < table.length; col++) {
+      let char = table[col][i];
+      if (char !== '.') {
+        if (colHash[char]) {
+          return false;
+        }
+        colHash[char] = 1;
+      }
+    }
+  }
+
+  const subboxes = [[0, 1, 2], [3, 4, 5], [6, 7, 8]];
+
+  for (let counter1 = 0; counter1 < 3; counter1++) {
+    for (let counter2 = 0; counter2 < 3; counter2++) {
+      const subboxHash = {};
+      for (let counter3 = 0; counter3 < 3; counter3++) {
+        for (let counter4 = 0; counter4 < 3; counter4++) {
+          let char = table[subboxes[counter1][counter3]][subboxes[counter2][counter4]];
+          if (char !== '.') {
+            if (subboxHash[char]) {
+              return false;
+            }
+            subboxHash[char] = 1;
+          }
+        }
+      }
+    }
+  }
+  return true;
 }
 
 module.exports = {
diff --git a/test/exercises.test.js b/test/exercises.test.js
index 93461ab..6dc6b24 100644
--- a/test/exercises.test.js
+++ b/test/exercises.test.js
@@ -137,7 +137,49 @@ describe("exercises", function() {
     });
   });
 
-  describe.skip("valid sudoku", function() {
+  describe("valid sudoku", function() {
+    it("is not valid if a row has duplicate values", function() {
+      // Arrange
+      const table = [
+        ["5","3",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".","5","5",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."]
+      ];
+
+       // Act
+      const valid = valid_sudoku(table);
+
+       // Assert
+      expect(valid).to.be.false;
+    });
+
+     it("is not valid if a column has duplicate values", function() {
+      // Arrange
+      const table = [
+        ["5",".",".",".",".",".",".",".","."],
+        ["2",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".","4",".",".",".","."],
+        [".",".",".",".","4",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."],
+        [".",".",".",".",".",".",".",".","."]
+      ];
+
+       // Act
+      const valid = valid_sudoku(table);
+
+       // Assert
+      expect(valid).to.be.false;
+    });
+
     it("works for the table given in the README", function() {
       // Arrange
       const table = [
@@ -156,7 +198,7 @@ describe("exercises", function() {
       const valid = valid_sudoku(table);
 
       // Assert
-      expect(valid).toEqual(true);
+      expect(valid).to.eql(true);
     });
 
     it("fails for the table given in the README", function() {
@@ -177,7 +219,7 @@ describe("exercises", function() {
       const valid = valid_sudoku(table);
 
       // Assert
-      expect(valid).toEqual(false);
+      expect(valid).to.eql(false);
     });
 
     it("fails for a duplicate number in a sub-box", function() {
@@ -198,7 +240,7 @@ describe("exercises", function() {
       const valid = valid_sudoku(table);
 
       // Assert
-      expect(valid).toEqual(false);
+      expect(valid).to.eql(false);
     });
 
     it("fails for a duplicate number in a bottom right sub-box", function() {
@@ -219,7 +261,7 @@ describe("exercises", function() {
       const valid = valid_sudoku(table);
 
       // Assert
-      expect(valid).toEqual(false);
+      expect(valid).to.eql(false);
     });
   });
 });