diff --git a/src/modules/checkIsValidUserInput.js b/src/modules/checkIsValidUserInput.js
index 40979664..47931d82 100644
--- a/src/modules/checkIsValidUserInput.js
+++ b/src/modules/checkIsValidUserInput.js
@@ -9,7 +9,12 @@
  * @return {boolean} - True if the user input is valid, false otherwise
  */
 function checkIsValidUserInput(userInput) {
-  /* Write your code here */
+  const isFourDigits = userInput.length === 4;
+  const hasUniqueDigits = new Set(userInput.split('')).size === 4;
+  const isNumber = !isNaN(+userInput);
+  const doesNotStartWithZero = userInput[0] !== '0';
+
+  return isFourDigits && hasUniqueDigits && isNumber && doesNotStartWithZero;
 }
 
 module.exports = {
diff --git a/src/modules/generateRandomNumber.js b/src/modules/generateRandomNumber.js
index 14ad1e2b..c4dd8345 100644
--- a/src/modules/generateRandomNumber.js
+++ b/src/modules/generateRandomNumber.js
@@ -7,7 +7,24 @@
  * @return {number} A random 4-digit number
  */
 function generateRandomNumber() {
-  /* Write your code here */
+  const digits = new Array(4);
+
+  digits[0] = Math.floor(1 + Math.random() * 9);
+
+  const usedDigits = new Set([digits[0]]);
+
+  for (let i = 1; i < 4; i++) {
+    let randomDigit;
+
+    do {
+      randomDigit = Math.floor(Math.random() * 10);
+    } while (usedDigits.has(randomDigit));
+
+    digits[i] = randomDigit;
+    usedDigits.add(randomDigit);
+  }
+
+  return Number(digits.join(''));
 }
 
 module.exports = {
diff --git a/src/modules/getBullsAndCows.js b/src/modules/getBullsAndCows.js
index 3f0b39a6..f8ee6b06 100644
--- a/src/modules/getBullsAndCows.js
+++ b/src/modules/getBullsAndCows.js
@@ -13,7 +13,23 @@
  * Example: { bulls: 1, cows: 2 }
  */
 function getBullsAndCows(userInput, numberToGuess) {
-  /* Write your code here */
+  const result = {
+    bulls: 0,
+    cows: 0,
+  };
+
+  const userNumber = userInput.toString();
+  const guessNumber = numberToGuess.toString();
+
+  for (let i = 0; i < userNumber.length; i++) {
+    if (userNumber[i] === guessNumber[i]) {
+      result.bulls++;
+    } else if (guessNumber.includes(userNumber[i])) {
+      result.cows++;
+    }
+  }
+
+  return result;
 }
 
 module.exports = {