diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..36d2f865d 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -12,4 +12,4 @@ 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..7ba8f4c75 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..d0b246f22 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -12,4 +12,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..6b3ef26b9 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,7 @@
-function contains() {}
+function contains(Obj, key) {
+  if (Obj === null || typeof Obj !== "object" || Array.isArray(Obj))
+    return false;
+  return Object.prototype.hasOwnProperty.call(Obj, key);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..0c4b1ced3 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -33,3 +33,19 @@ test.todo("contains on empty object returns false");
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toEqual(false);
+});
+
+test("returns true when property exists", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toEqual(true);
+});
+
+test("returns false when property does not exist", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toEqual(false);
+});
+
+test("returns false for invalid input like array", () => {
+  expect(contains([1, 2, 3], "0")).toEqual(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..3281fdf20 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,8 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  if (!Array.isArray(countryCurrencyPairs)) {
+    return {};
+  }
+  return Object.fromEntries(countryCurrencyPairs);
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..d92c73101 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -33,3 +33,40 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+test("returns empty object for empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
+
+test("creates lookup from country-currency pairs", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
+
+test("handles single pair", () => {
+  expect(createLookup([["JP", "JPY"]])).toEqual({
+    JP: "JPY",
+  });
+});
+
+test("overwrites duplicate country codes (last one wins)", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["US", "USN"],
+    ])
+  ).toEqual({
+    US: "USN",
+  });
+});
+
+test("handles invalid input (non-array)", () => {
+  expect(createLookup(null)).toEqual({});
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..0872f83fa 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,21 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
+
+  if (!queryString) return queryParams;
+
+  if (queryString.startsWith("?")) {
+    queryString = queryString.slice(1);
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (!pair) continue;
+
+    const [rawKey, ...rawValue] = pair.split("=");
+    const key = decodeURIComponent(rawKey);
+    const value = decodeURIComponent(rawValue.join("="));
+
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..e6b0e31df 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,10 +3,69 @@
 // 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",
+    equation: "x=y+1",
+  });
+});
+test("parses simple key-value pairs", () => {
+  expect(parseQueryString("name=alice&age=25")).toEqual({
+    name: "alice",
+    age: "25",
+  });
+});
+test("strips leading question marks", () => {
+  expect(parseQueryString("?user=bob&status=active")).toEqual({
+    user: "bob",
+    status: "active",
+  });
+});
+test("returns empty object for empty string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("returns empty object for null or undefined", () => {
+  expect(parseQueryString(null)).toEqual({});
+  expect(parseQueryString(undefined)).toEqual({});
+});
+test("decodes URL encoded keys and values", () => {
+  expect(parseQueryString("search=coding%20tutorials&city=New%20York")).toEqual(
+    {
+      search: "coding tutorials",
+      city: "New York",
+    }
+  );
+});
+
+test("decodes complex characters and emojis", () => {
+  expect(parseQueryString("item=%F0%9F%8D%95&price=%2410")).toEqual({
+    item: "🍕",
+    price: "$10",
+  });
+});
+test("ignores empty segments from double ampersands", () => {
+  expect(parseQueryString("a=1&&b=2")).toEqual({
+    a: "1",
+    b: "2",
+  });
+});
+
+test("ignores trailing ampersands", () => {
+  expect(parseQueryString("a=1&b=2&")).toEqual({
+    a: "1",
+    b: "2",
+  });
+});
+test("handles keys with empty values", () => {
+  expect(parseQueryString("key=")).toEqual({
+    key: "",
+  });
+});
+
+test("handles keys without an equals sign", () => {
+  expect(parseQueryString("flag")).toEqual({
+    flag: "",
   });
 });
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..94a6da1cb 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,11 @@
-function tally() {}
+function tally(array) {
+  const tally = {};
+  if (!Array.isArray(array)) throw new TypeError("Expected an array");
+  if (array.length === 0) return tally;
+  for (const item of array) {
+    tally[item] = (tally[item] || 0) + 1;
+  }
+  return tally;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..6b0888faf 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -24,6 +24,9 @@ const tally = require("./tally.js");
 // When passed to tally
 // Then it should return an empty object
 test.todo("tally on an empty array returns an empty object");
+test("Empty array of items", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
@@ -32,3 +35,23 @@ test.todo("tally on an empty array returns an empty object");
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+
+test("Invalid input", () => {
+  expect(() => tally("not an array")).toThrow(TypeError);
+});
+test("Test duplicate array", () => {
+  const duplicatesArray = [
+    "apple",
+    "banana",
+    "apple",
+    "orange",
+    "banana",
+    "apple",
+  ];
+  const result = tally(duplicatesArray);
+  expect(result).toEqual({
+    apple: 3,
+    banana: 2,
+    orange: 1,
+  });
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..f35a148fa 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -5,7 +5,7 @@
 // Then it should swap the keys and values in the object
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
-
+/*
 function invert(obj) {
   const invertedObj = {};
 
@@ -17,13 +17,33 @@ function invert(obj) {
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+//{ key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+//{ key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+//The target return value is { "1": "a", "2": "b" }.
 
 // c) What does Object.entries return? Why is it needed in this program?
+//It returns An array of the object's own property [key, value] pairs.
+// It allows the for...of loop to easily access both the key and the value at the same time during each iteration.
 
 // d) Explain why the current return value is different from the target output
+//Using invertedObj.key creates a literal property named "key" on the object. 
+// To use the value inside the key variable, you must use bracket notation: invertedObj[key].
+//The function is setting the original value to the key. 
+// To actually "invert" the object, it needs to swap them: invertedObj[value] = key;.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+*/
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+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..5f879e88e
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,24 @@
+const invert = require("./invert.js");
+test("inverts a single key-value pair", () => {
+  const input = { a: 1 };
+  expect(invert(input)).toEqual({ 1: "a" });
+});
+test("inverts multiple key-value pairs", () => {
+  const input = { a: 1, b: 2, c: 3 };
+  const expected = { 1: "a", 2: "b", 3: "c" };
+
+  expect(invert(input)).toEqual(expected);
+});
+test("returns empty object for empty input", () => {
+  expect(invert({})).toEqual({});
+});
+test("overwrites keys when duplicate values exist", () => {
+  const input = { a: 1, b: 1 };
+  expect(invert(input)).toEqual({ 1: "b" });
+});
+test("turns boolean and null values into string keys", () => {
+  const input = { a: true, b: null };
+  const expected = { true: "a", null: "b" };
+
+  expect(invert(input)).toEqual(expected);
+});