diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..4ddf31650 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,8 @@
 // Predict and explain first...
+// My prediction: the code will show an Error or "undefined", the Object is fine but
+// called in a wrong way in the last line. we cant use object[number] to get a value
+// withing an Object, that works only with arrays. Instead, we need to write
+// the name of the key that we need.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +16,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address["houseNumber"]}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..419c6b040 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// Prediction: the code will throw an error
+// Explanation: An object can not be used or accessed as an array.
 
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for ( const key in author ) {
+console.log(author[key]);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..036a2def4 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,15 +1,17 @@
-// Predict and explain first...
+  // Predict and explain first...
+  // to separate the ingredients in different lines we need to use the function: join()
+  // the ingredients is an array not an object, so we can use join() and pass "\n" to put
+  // new line between every item.
 
-// This program should log out the title, how many it serves and the ingredients.
-// Each ingredient should be logged on a new line
-// How can you fix it?
+  // This program should log out the title, how many it serves and the ingredients.
+  // Each ingredient should be logged on a new line
+  // How can you fix it?
 
-const recipe = {
-  title: "bruschetta",
-  serves: 2,
-  ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
-};
+  const recipe = {
+    title: "bruschetta",
+    serves: 2,
+    ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
+  };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+  console.log(`Title: ${recipe.title} || serves: ${recipe.serves}
+ingredients: \n ${recipe.ingredients.join("\n ")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..a4dc924eb 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, find) {
+
+  if(typeof obj !== 'object' || !obj || Array.isArray(obj)) {
+    return false;
+  }
+  return obj.hasOwnProperty(find);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..b1c430654 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -2,7 +2,7 @@ const contains = require("./contains.js");
 
 /*
 Implement a function called contains that checks an object contains a
-particular property
+particular property 
 
 E.g. contains({a: 1, b: 2}, 'a') // returns true
 as the object contains a key of 'a'
@@ -16,20 +16,47 @@ as the object doesn't contains a key of 'c'
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test.todo("contains on empty object returns false");
+test("When the object contains the property return true, false otherwise", () => {
+    expect(contains({a: 1, b: 2, c: 3}, "a")).toBe(true);
+    expect(contains({a: 1, b: 2, c: 3}, "d")).toBe(false);
+})
 
 // Given an empty object
 // When passed to contains
 // Then it should return false
 test.todo("contains on empty object returns false");
+test("if contains on empty object returns false", () => {
+    expect(contains({}, "a")).toBe(false);
+    expect(contains({}, "Hello")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test.todo("if contains on object with existing property returns true");
+test("if contains on object with existing property returns true", () => {
+    expect(contains({m: 10, s: 20, w: 5}, "s")).toBe(true);
+    expect(contains({x: 100, y: 200, z: 300}, "z")).toBe(true);
+    expect(contains({name: "Ahmed", age: 30}, "name")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test.todo("if contains on object with non-existent property returns false");
+test("if contains on object with non-existent property returns false", () => {
+    expect(contains({m: 10, s: 20, w: 5}, "x")).toBe(false);
+    expect(contains({num1: 100, num2: 200, num3: 300}, "num5")).toBe(false);
+    expect(contains({name: "Ahmed", age: 30}, "address")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test.todo("if contains with invalid parameters returns false or throws an error");
+test("if contains with invalid parameters returns false or throws an error", () => {
+    expect(contains(['a','b','c'], "1")).toBe(false);
+    expect(contains("string", "a")).toBe(false);
+    expect(contains(12345, "a")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..609b1acc9 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
-}
+function createLookup(arrayOfPairs) {
+  let obj = {};
+ 
+  for (let i = 0; i < arrayOfPairs.length; i++) {
+    const [key, value] = arrayOfPairs[i];
+    obj[key] = value;
+    }
+  return obj;
+};
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..73bf81150 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,14 @@
 const createLookup = require("./lookup.js");
 
 test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () => {
+  expect(createLookup([['US', 'USD'], ['CA', 'CAD'], ['GB', 'GBP'], ['JP', 'JPY']])).toEqual({
+    'US': 'USD',
+    'CA': 'CAD',
+    'GB': 'GBP',
+    'JP': 'JPY'
+  });
+});
 
 /*
 
@@ -21,7 +29,7 @@ Then
  - The values are the corresponding currency codes
 
 Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
+Given: [['US', 'USD'], ['CA', 'CAD']] 
 
 When
 createLookup(countryCurrencyPairs) is called
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..2d0e478a7 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,16 +1,25 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
-  }
-  const keyValuePairs = queryString.split("&");
+  if (!queryString) return queryParams;
+
+  const pairs = queryString.split("&");
+  
+  for (const pair of pairs) {
+    const eqIndex = pair.indexOf("=");
+    
+    let key, value;
+    if (eqIndex === -1) {
+      key = decodeURIComponent(pair);
+      value = "";
+    } else {
+      key = decodeURIComponent(pair.slice(0, eqIndex));
+      value = decodeURIComponent(pair.slice(eqIndex + 1));
+    }
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;
\ No newline at end of file
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..c8710fd0d 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,10 +3,38 @@
 // Below is one test case for an edge case the implementation doesn't handle well.
 // Fix the implementation for this test, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js") 
 
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
     "equation": "x=y+1",
   });
 });
+
+test("parses empty querystring", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses single key-value pair", () => {
+  expect(parseQueryString("name=John")).toEqual({
+    "name": "John",
+  });
+});
+
+test("parses key with empty value", () => {
+  expect(parseQueryString("key=")).toEqual({
+    "key": "",
+  });
+});
+
+test("parses empty key with value", () => {
+  expect(parseQueryString("=value")).toEqual({
+    "": "value",
+  });
+});
+
+test("parses key without '=' separator", () => {
+  expect(parseQueryString("key")).toEqual({
+    "key": "",
+  });
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..56967e691 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,16 @@
-function tally() {}
+function tally(arr) {
+    let obj = Object.create(null);
+    if (!Array.isArray(arr)) {
+        throw new Error("Input must be an array");
+    }
 
-module.exports = tally;
+    for (let i = 0; i < arr.length; i++) {
+        if (!obj[arr[i]])
+            obj[arr[i]] = 1;
+        else
+            obj[arr[i]]++;
+    }
+    return obj;
+}
+
+module.exports = tally; 
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..3f6f6dda4 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,38 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test.todo("when passed an array of items, it returns an object with counts for each unique item");
+test("when passed an array of items, it returns an object with counts for each unique item", () => {
+    const input = ['a', 'a', 'b', 'c'];
+    const expectedOutput = { a: 2, b: 1, c: 1 };
+    expect(tally(input)).toEqual(expectedOutput);
+});
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
 test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+    const input = [];
+    const expectedOutput = {};
+    expect(tally(input)).toEqual(expectedOutput);
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test.todo("tally counts each unique item in an array with duplicates");
+test("tally counts each unique item in an array with duplicates", () => {
+    const input = ['x', 'y', 'x', 'z', 'y', 'x'];
+    const expectedOutput = { x: 3, y: 2, z: 1 };
+    expect(tally(input)).toEqual(expectedOutput);
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test.todo("tally throws an error when passed invalid input");
+test("tally throws an error when passed invalid input", () => {
+    const input = "invalid input";
+    expect(() => tally(input)).toThrow("Input must be an array");
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..1513034a7 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,30 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+// the current return value is { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// the current return value is { key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// the target return value should be { '1': 'a', '2': 'b' }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// it returns an array of a given object in [key, value] pairs.
 
 // d) Explain why the current return value is different from the target output
+// because in the loop, it always assigns the property 'key' to the value,
+// so the final result only contains one property 'key' with the last value assigned in the loop.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Code fixed.
+
+console.log(invert({ a: 1 })); // { '1': 'a' }
+module.exports = invert;
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..c056cf6ad
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,9 @@
+test.todo("check if invert function swaps keys and values");
+test("check if invert function swaps keys and values", () => {
+  const invert = require("./invert");
+
+  expect(invert({ a: 1 })).toEqual({ '1': 'a' });
+  expect(invert({ a: 1, b: 2 })).toEqual({ '1': 'a', '2': 'b' });
+  expect(invert({ x: 10, y: 20 })).toEqual({ '10': 'x', '20': 'y' });
+  expect(invert({})).toEqual({});
+});
\ No newline at end of file
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..4e8294866 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,25 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(string) {
+  let outputObject = Object.create(null);
+  let splitString = string.split(" ");
+  
+  for ( let i = 0; i < splitString.length; i++) {
+    let word = splitString[i].toLowerCase();
+        word = word.replace(/[.,!?]/g, '');
+
+    if (word.length != 0) {
+        if (!outputObject[word])
+          outputObject[word] = 1;
+        else
+          outputObject[word]++;
+    }
+  }
+
+  return outputObject;
+}
+console.log(countWords("Hello,World! Hello World!"));
+console.log(countWords("constructor constructor"));
+console.log(countWords("          Hello World      "));
\ No newline at end of file