diff --git a/account-analytics/src/main/java/com.bobocode/AccountAnalytics.java b/account-analytics/src/main/java/com.bobocode/AccountAnalytics.java
index 8c825fb..0b7bdff 100644
--- a/account-analytics/src/main/java/com.bobocode/AccountAnalytics.java
+++ b/account-analytics/src/main/java/com.bobocode/AccountAnalytics.java
@@ -2,10 +2,17 @@
 
 import com.bobocode.exception.EntityNotFoundException;
 import com.bobocode.model.Account;
+import com.bobocode.model.Sex;
 
 import java.math.BigDecimal;
 import java.time.Month;
 import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+import static java.util.Comparator.comparing;
+import static java.util.function.Function.identity;
+import static java.util.stream.Collectors.*;
 
 import static java.util.stream.Collectors.mapping;
 import static java.util.stream.Collectors.toMap;
@@ -30,7 +37,8 @@ private AccountAnalytics(Collection<Account> accounts) {
      * @return account with max balance wrapped with optional
      */
     public Optional<Account> findRichestPerson() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .max(comparing(Account::getBalance));
     }
 
     /**
@@ -40,7 +48,9 @@ public Optional<Account> findRichestPerson() {
      * @return a list of accounts
      */
     public List<Account> findAccountsByBirthdayMonth(Month birthdayMonth) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .filter(a -> a.getBirthday().getMonth().equals(birthdayMonth))
+                .collect(toList());
     }
 
     /**
@@ -50,7 +60,8 @@ public List<Account> findAccountsByBirthdayMonth(Month birthdayMonth) {
      * @return a map where key is true or false, and value is list of male, and female accounts
      */
     public Map<Boolean, List<Account>> partitionMaleAccounts() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(partitioningBy(a -> a.getSex().equals(Sex.MALE)));
     }
 
     /**
@@ -60,7 +71,8 @@ public Map<Boolean, List<Account>> partitionMaleAccounts() {
      * @return a map where key is an email domain and value is a list of all account with such email
      */
     public Map<String, List<Account>> groupAccountsByEmailDomain() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(groupingBy(a -> a.getEmail().split("@")[1]));
     }
 
     /**
@@ -69,7 +81,9 @@ public Map<String, List<Account>> groupAccountsByEmailDomain() {
      * @return total number of letters of first and last names of all accounts
      */
     public int getNumOfLettersInFirstAndLastNames() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .mapToInt(a -> a.getFirstName().length() + a.getLastName().length())
+                .sum();
     }
 
     /**
@@ -78,7 +92,9 @@ public int getNumOfLettersInFirstAndLastNames() {
      * @return total balance of all accounts
      */
     public BigDecimal calculateTotalBalance() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .map(Account::getBalance)
+                .reduce(BigDecimal.ZERO, BigDecimal::add);
     }
 
     /**
@@ -87,7 +103,10 @@ public BigDecimal calculateTotalBalance() {
      * @return list of accounts sorted by first and last names
      */
     public List<Account> sortByFirstAndLastNames() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .sorted(comparing(Account::getFirstName)
+                        .thenComparing(Account::getLastName))
+                .collect(toList());
     }
 
     /**
@@ -97,7 +116,9 @@ public List<Account> sortByFirstAndLastNames() {
      * @return true if there is an account that has an email with provided domain
      */
     public boolean containsAccountWithEmailDomain(String emailDomain) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .map(Account::getEmail)
+                .anyMatch(email -> email.split("@")[1].equals(emailDomain));
     }
 
     /**
@@ -108,7 +129,11 @@ public boolean containsAccountWithEmailDomain(String emailDomain) {
      * @return account balance
      */
     public BigDecimal getBalanceByEmail(String email) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .filter(account -> account.getEmail().equals(email))
+                .findFirst()
+                .map(Account::getBalance)
+                .orElseThrow(() -> new EntityNotFoundException(String.format("Cannot find Account by email=%s", email)));
     }
 
     /**
@@ -117,7 +142,8 @@ public BigDecimal getBalanceByEmail(String email) {
      * @return map of accounts by its ids
      */
     public Map<Long, Account> collectAccountsById() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(toMap(Account::getId, identity()));
     }
 
     /**
@@ -128,7 +154,9 @@ public Map<Long, Account> collectAccountsById() {
      * @return map of account by its ids the were created in a particular year
      */
     public Map<String, BigDecimal> collectBalancesByIdForAccountsCreatedOn(int year) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .filter(account -> account.getCreationDate().getYear() == year)
+                .collect(toMap(Account::getEmail, Account::getBalance));
     }
 
     /**
@@ -138,7 +166,8 @@ public Map<String, BigDecimal> collectBalancesByIdForAccountsCreatedOn(int year)
      * @return a map where key is a last name and value is a set of first names
      */
     public Map<String, Set<String>> groupFirstNamesByLastNames() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(groupingBy(Account::getLastName, mapping(Account::getFirstName, toSet())));
     }
 
     /**
@@ -148,7 +177,9 @@ public Map<String, Set<String>> groupFirstNamesByLastNames() {
      * @return a map where a key is a birthday month and value is comma-separated first names
      */
     public Map<Month, String> groupCommaSeparatedFirstNamesByBirthdayMonth() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(groupingBy(a -> a.getBirthday().getMonth(),
+                        mapping(Account::getFirstName, joining(", "))));
     }
 
     /**
@@ -158,7 +189,10 @@ public Map<Month, String> groupCommaSeparatedFirstNamesByBirthdayMonth() {
      * @return a map where key is a creation month and value is total balance of all accounts created in that month
      */
     public Map<Month, BigDecimal> groupTotalBalanceByCreationMonth() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .collect(groupingBy(a -> a.getCreationDate().getMonth(),
+                        mapping(Account::getBalance,
+                                reducing(BigDecimal.ZERO, BigDecimal::add))));
     }
 
     /**
@@ -168,7 +202,11 @@ public Map<Month, BigDecimal> groupTotalBalanceByCreationMonth() {
      * @return a map where key is a letter and value is its count in all first names
      */
     public Map<Character, Long> getCharacterFrequencyInFirstNames() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .map(Account::getFirstName)
+                .flatMapToInt(String::chars)
+                .mapToObj(c -> (char) c)
+                .collect(groupingBy(identity(), counting()));
     }
 
     /**
@@ -178,7 +216,12 @@ public Map<Character, Long> getCharacterFrequencyInFirstNames() {
      * @return a map where key is a letter and value is its count ignoring case in all first and last names
      */
     public Map<Character, Long> getCharacterFrequencyIgnoreCaseInFirstAndLastNames() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return accounts.stream()
+                .flatMap(a -> Stream.of(a.getFirstName(), a.getLastName()))
+                .map(String::toLowerCase)
+                .flatMapToInt(String::chars)
+                .mapToObj(c -> (char) c)
+                .collect(groupingBy(identity(), counting()));
     }
 
 }
diff --git a/crazy-lambdas/src/main/java/com/bobocode/CrazyLambdas.java b/crazy-lambdas/src/main/java/com/bobocode/CrazyLambdas.java
index 966d72c..6a329f1 100644
--- a/crazy-lambdas/src/main/java/com/bobocode/CrazyLambdas.java
+++ b/crazy-lambdas/src/main/java/com/bobocode/CrazyLambdas.java
@@ -1,8 +1,8 @@
 package com.bobocode;
 
 import java.math.BigDecimal;
+import java.util.concurrent.ThreadLocalRandom;
 import java.util.Map;
-import java.util.TreeMap;
 import java.util.function.*;
 
 public class CrazyLambdas {
@@ -13,7 +13,7 @@ public class CrazyLambdas {
      * @return a string supplier
      */
     public static Supplier<String> helloSupplier() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return () -> "Hello";
     }
 
     /**
@@ -22,7 +22,7 @@ public static Supplier<String> helloSupplier() {
      * @return a string predicate
      */
     public static Predicate<String> isEmptyPredicate() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return String::isEmpty;
     }
 
     /**
@@ -32,7 +32,7 @@ public static Predicate<String> isEmptyPredicate() {
      * @return function that repeats Strings
      */
     public static BiFunction<String, Integer, String> stringMultiplier() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return String::repeat;
     }
 
     /**
@@ -42,7 +42,7 @@ public static BiFunction<String, Integer, String> stringMultiplier() {
      * @return function that converts adds dollar sign
      */
     public static Function<BigDecimal, String> toDollarStringFunction() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return bigDecimal -> "$" + bigDecimal;
     }
 
     /**
@@ -54,7 +54,7 @@ public static Function<BigDecimal, String> toDollarStringFunction() {
      * @return a string predicate
      */
     public static Predicate<String> lengthInRangePredicate(int min, int max) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return str -> str.length() >= min && str.length() < max;
     }
 
     /**
@@ -63,7 +63,7 @@ public static Predicate<String> lengthInRangePredicate(int min, int max) {
      * @return int supplier
      */
     public static IntSupplier randomIntSupplier() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return () -> ThreadLocalRandom.current().nextInt();
     }
 
 
@@ -73,7 +73,7 @@ public static IntSupplier randomIntSupplier() {
      * @return int operation
      */
     public static IntUnaryOperator boundedRandomIntSupplier() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return bound -> ThreadLocalRandom.current().nextInt(bound);
     }
 
     /**
@@ -82,7 +82,7 @@ public static IntUnaryOperator boundedRandomIntSupplier() {
      * @return square operation
      */
     public static IntUnaryOperator intSquareOperation() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return a -> a * a;
     }
 
     /**
@@ -91,7 +91,7 @@ public static IntUnaryOperator intSquareOperation() {
      * @return binary sum operation
      */
     public static LongBinaryOperator longSumOperation() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return (a, b) -> a + b;
     }
 
     /**
@@ -100,7 +100,7 @@ public static LongBinaryOperator longSumOperation() {
      * @return string to int converter
      */
     public static ToIntFunction<String> stringToIntConverter() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return Integer::parseInt;
     }
 
     /**
@@ -111,7 +111,7 @@ public static ToIntFunction<String> stringToIntConverter() {
      * @return a function supplier
      */
     public static Supplier<IntUnaryOperator> nMultiplyFunctionSupplier(int n) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return () -> a -> n * a;
     }
 
     /**
@@ -120,7 +120,7 @@ public static Supplier<IntUnaryOperator> nMultiplyFunctionSupplier(int n) {
      * @return function that composes functions with trim() function
      */
     public static UnaryOperator<Function<String, String>> composeWithTrimFunction() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return stringFunction -> stringFunction.compose(String::trim);
     }
 
     /**
@@ -131,7 +131,11 @@ public static UnaryOperator<Function<String, String>> composeWithTrimFunction()
      * @return a thread supplier
      */
     public static Supplier<Thread> runningThreadSupplier(Runnable runnable) {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return () -> {
+            Thread thread = new Thread(runnable);
+            thread.start();
+            return thread;
+        };
     }
 
     /**
@@ -140,7 +144,7 @@ public static Supplier<Thread> runningThreadSupplier(Runnable runnable) {
      * @return a runnable consumer
      */
     public static Consumer<Runnable> newThreadRunnableConsumer() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return runnable -> new Thread(runnable).start();
     }
 
     /**
@@ -150,7 +154,11 @@ public static Consumer<Runnable> newThreadRunnableConsumer() {
      * @return a function that transforms runnable into a thread supplier
      */
     public static Function<Runnable, Supplier<Thread>> runnableToThreadSupplierFunction() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return runnable -> () -> {
+            Thread thread = new Thread(runnable);
+            thread.start();
+            return thread;
+        };
     }
 
     /**
@@ -163,7 +171,7 @@ public static Function<Runnable, Supplier<Thread>> runnableToThreadSupplierFunct
      * @return a binary function that receiver predicate and function and compose them to create a new function
      */
     public static BiFunction<IntUnaryOperator, IntPredicate, IntUnaryOperator> functionToConditionalFunction() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return (intOperation, intPredicate) -> a -> intPredicate.test(a) ? intOperation.applyAsInt(a) : a;
     }
 
     /**
@@ -174,7 +182,7 @@ public static BiFunction<IntUnaryOperator, IntPredicate, IntUnaryOperator> funct
      * @return a high-order function that fetches a function from a function map by a given name or returns identity()
      */
     public static BiFunction<Map<String, IntUnaryOperator>, String, IntUnaryOperator> functionLoader() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return (functionMap, functionName) -> functionMap.getOrDefault(functionName, IntUnaryOperator.identity());
     }
 
     /**
@@ -183,7 +191,8 @@ public static BiFunction<Map<String, IntUnaryOperator>, String, IntUnaryOperator
      * @return a supplier instance
      */
     public static Supplier<Supplier<Supplier<String>>> trickyWellDoneSupplier() {
-        throw new UnsupportedOperationException("It's your job to implement this method"); // todo
+        return () -> () -> () -> "WELL DONE!";
     }
 }
 
+
diff --git a/math-functions/src/main/java/com.bobocode/Functions.java b/math-functions/src/main/java/com.bobocode/Functions.java
index 80ebc20..f983960 100644
--- a/math-functions/src/main/java/com.bobocode/Functions.java
+++ b/math-functions/src/main/java/com.bobocode/Functions.java
@@ -1,5 +1,7 @@
 package com.bobocode;
 
+import static java.lang.Math.abs;
+
 public class Functions {
     /**
      * A static factory method that creates an integer function map with basic functions:
@@ -14,7 +16,11 @@ public class Functions {
     public static FunctionMap<Integer, Integer> intFunctionMap() {
         FunctionMap<Integer, Integer> intFunctionMap = new FunctionMap<>();
 
-        // todo: add simple functions to the function map (abs, sng, increment, decrement, square)
+        intFunctionMap.addFunction("square", n -> n * n);
+        intFunctionMap.addFunction("abs", Math::abs);
+        intFunctionMap.addFunction("increment", n -> n + 1);
+        intFunctionMap.addFunction("decrement", n -> n - 1);
+        intFunctionMap.addFunction("sgn", n -> (n != 0) ? n / abs(n) : 0);
 
         return intFunctionMap;
     }
diff --git a/sum-of-squares/src/main/java/com/bobocode/SumOfSquares.java b/sum-of-squares/src/main/java/com/bobocode/SumOfSquares.java
index fc0dfde..56736c2 100644
--- a/sum-of-squares/src/main/java/com/bobocode/SumOfSquares.java
+++ b/sum-of-squares/src/main/java/com/bobocode/SumOfSquares.java
@@ -3,6 +3,8 @@
 
 import com.bobocode.exception.InvalidRangeException;
 
+import java.util.stream.IntStream;
+
 
 /**
  * This class allow to calculate a sum of squares of integer number in a certain range. It was implemented using
@@ -17,7 +19,7 @@ public static void main(String[] args) {
      * This method calculates the sum of squares of integer in the range
      *
      * @param startInclusive first element in range
-     * @param endInclusive last element in range
+     * @param endInclusive   last element in range
      * @return the sum of squares of each element in the range
      */
     static int calculateSumOfSquaresInRange(int startInclusive, int endInclusive) {
@@ -25,11 +27,8 @@ static int calculateSumOfSquaresInRange(int startInclusive, int endInclusive) {
             throw new InvalidRangeException();
         }
 
-        // todo: refactor using functional approach
-        int sumOfSquares = 0;
-        for (int i = startInclusive; i <= endInclusive; i++) {
-            sumOfSquares += i * i;
-        }
-        return sumOfSquares;
+        return IntStream.rangeClosed(startInclusive, endInclusive)
+                .map(a -> a * a)
+                .sum();
     }
 }

<!DOCTYPE html PUBLIC '-//W3C//DTD XHTML 1.0 Transitional//EN' 'http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd'>
<html xmlns='http://www.w3.org/1999/xhtml'>
<head>
<title>pFad - Phonifier reborn</title>
<meta http-equiv='Content-Type' content='text/html; charset=utf-8' />
</head>
<body>
<h1>Pfad - The Proxy pFad of &#169; 2024 Garber Painting. All rights reserved.</h1>


<!-- Disclaimer -->
<p>Note: This service is not intended for secure transactions such as banking, social media, email, or purchasing. Use at your own risk. We assume no liability whatsoever for broken pages.</p>
<br>
<p>Alternative Proxies:</p><p><a href="http://rainy.clevelandohioweatherforecast.com/php-proxy/index.php?q=https://patch-diff.githubusercontent.com/raw/bobocode-projects/java-functional-features-exercises/pull/2.diff" target="_blank">Alternative Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/index.php?u=https://patch-diff.githubusercontent.com/raw/bobocode-projects/java-functional-features-exercises/pull/2.diff" target="_blank">pFad Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v3index.php?u=https://patch-diff.githubusercontent.com/raw/bobocode-projects/java-functional-features-exercises/pull/2.diff" target="_blank">pFad v3 Proxy</a></p><p><a href="http://rainy.clevelandohioweatherforecast.com/pFad/v4index.php?u=https://patch-diff.githubusercontent.com/raw/bobocode-projects/java-functional-features-exercises/pull/2.diff" target="_blank">pFad v4 Proxy</a></p></body>
</html>