solved the problem

Splitwise/Client.java

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+package Designs.Splitwise;
+
+// https://workat.tech/machine-coding/practice/splitwise-problem-0kp2yneec2q2
+
+import Designs.Splitwise.machine.Machine;
+import Designs.Splitwise.machine.Splitwise;
+import Designs.Splitwise.model.User;
+import Designs.Splitwise.modeselector.SplitModeSelector;
+import Designs.Splitwise.modeselector.SplitTypes;
+import Designs.Splitwise.parser.Parser;
+import Designs.Splitwise.splitmodes.EqualSplitMode;
+import Designs.Splitwise.splitmodes.ExactSplitMode;
+import Designs.Splitwise.splitmodes.PercentSplitMode;
+
+import java.util.HashMap;
+import java.util.Map;
+
+//You can create a few users in your main method. No need to take it as input.
+//There will be 3 types of input:
+//SplitTypes in the format: EXPENSE <user-id-of-person-who-paid> <no-of-users> <space-separated-list-of-users> <EQUAL/EXACT/PERCENT> <space-separated-values-in-case-of-non-equal>
+//Show balances for all: SHOW
+//Show balances for a single user: SHOW <user-id>
+
+//SHOW
+//SHOW u1
+//EXPENSE u1 1000 4 u1 u2 u3 u4 EQUAL
+//SHOW u4
+//SHOW u1
+//EXPENSE u1 1250 2 u2 u3 EXACT 370 880
+//SHOW
+//EXPENSE u4 1200 4 u1 u2 u3 u4 PERCENT 40 20 20 20
+//SHOW u1
+//SHOW
+public class Client {
+    public static void main(String[] args) {
+        // onboard users in the machine
+        User u1 = new User("u1", "jack", "jack@gmail.com", 9289);
+        User u2 = new User("u2", "Tom", "tom@gmail.com", 9282);
+        User u3 = new User("u3", "kev", "kev@gmail.com", 9281);
+        User u4 = new User("u4", "rees", "rees@gmail.com", 9280);
+
+        Map<String, User> usersMap = new HashMap<>();
+        usersMap.put(u1.getUserId(), u1);
+        usersMap.put(u2.getUserId(), u2);
+        usersMap.put(u3.getUserId(), u3);
+        usersMap.put(u4.getUserId(), u4);
+
+        // initialise SplitModeSelector
+        SplitModeSelector splitModeSelector = new SplitModeSelector(
+                Map.of(SplitTypes.EQUAL, new EqualSplitMode(),
+                        SplitTypes.EXACT, new ExactSplitMode(),
+                        SplitTypes.PERCENT, new PercentSplitMode()
+                ));
+
+        // Initialise Machine
+        Machine machine = new Splitwise(usersMap, splitModeSelector);
+
+        // Commands
+        String equalExpense = "EXPENSE u1 1000 4 u1 u2 u3 u4 EQUAL";
+        String exactExpense = "EXPENSE u1 1250 2 u2 u3 EXACT 370 880";
+        String percentExpense = "EXPENSE u4 1200 4 u1 u2 u3 u4 PERCENT 40 20 20 20";
+        String show = "SHOW";
+        String show_u1 = "SHOW u1";
+        String show_u4 = "SHOW u4";
+
+        // Input to Parser
+        Parser parser = new Parser(machine);
+        parser.parse(equalExpense);
+        parser.parse(show_u4);
+        parser.parse(show_u1);
+        parser.parse(exactExpense);
+        parser.parse(show);
+        parser.parse(percentExpense);
+        parser.parse(show_u1);
+        parser.parse(show);
+    }
+}

Splitwise/machine/Machine.java

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+package Designs.Splitwise.machine;
+
+public interface Machine {
+    void showAll();
+
+    void showBalanceFor(String userId);
+
+    void addExpense(String[] tokens);
+}

Splitwise/machine/Splitwise.java

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+package Designs.Splitwise.machine;
+
+import Designs.Splitwise.model.User;
+import Designs.Splitwise.splitmodes.SplitMode;
+import Designs.Splitwise.modeselector.SplitModeSelector;
+import Designs.Splitwise.modeselector.SplitTypes;
+
+import java.util.Map;
+
+public class Splitwise implements Machine {
+    private Map<String, User> usersMap;
+    private SplitModeSelector modeSelector;
+
+    public Splitwise(Map<String, User> usersMap, SplitModeSelector modeSelector) {
+        this.usersMap = usersMap;
+        this.modeSelector = modeSelector;
+    }
+
+    @Override
+    public void showAll() {
+        for (Map.Entry<String, User> entry : usersMap.entrySet()) {
+            User user = entry.getValue();
+            user.showDebt();
+        }
+    }
+
+    @Override
+    public void showBalanceFor(String userId) {
+        User user = usersMap.get(userId);
+        if (user == null) System.out.println("User not found");
+        user.showDebt();
+        user.showLoan();
+    }
+
+    @Override
+    public void addExpense(String[] tokens) {
+        int userLength = Integer.parseInt(tokens[3]);
+        SplitTypes splitType = SplitTypes.valueOf(tokens[4 + userLength]);
+
+        SplitMode mode = modeSelector.select(splitType);
+        mode.addExpense(usersMap, tokens);
+    }
+}

Splitwise/model/User.java

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+package Designs.Splitwise.model;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class User {
+    private final String userId;
+    private final String name;
+    private final String email;
+    private final Integer mobileNumber;
+    private final Map<User, Double> debtMap;
+    private final Map<User, Double> loanMap;
+
+    public User(String userId, String name, String email, Integer mobileNumber) {
+        this.userId = userId;
+        this.name = name;
+        this.email = email;
+        this.mobileNumber = mobileNumber;
+        this.debtMap = new HashMap<>();
+        this.loanMap = new HashMap<>();
+    }
+
+    public String getUserId() {
+        return userId;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof User)) return false;
+
+        User user = (User) o;
+
+        if (!userId.equals(user.userId)) return false;
+        if (!getName().equals(user.getName())) return false;
+        if (!email.equals(user.email)) return false;
+        return mobileNumber.equals(user.mobileNumber);
+    }
+
+    @Override
+    public int hashCode() {
+        int result = userId.hashCode();
+        result = 31 * result + getName().hashCode();
+        result = 31 * result + email.hashCode();
+        result = 31 * result + mobileNumber.hashCode();
+        return result;
+    }
+
+    public Double debtFrom(User user) {
+        return debtMap.getOrDefault(user, 0.0);
+    }
+
+    public Double loanGivenTo(User user) {
+        return loanMap.getOrDefault(user, 0.0);
+    }
+
+    public void addLoanFor(User user, Double balance) {
+        loanMap.put(user, balance);
+    }
+
+    public void addDebtFor(User user, Double balance) {
+        debtMap.put(user, balance);
+    }
+
+    public void removeDebtFor(User user) {
+        debtMap.remove(user);
+    }
+
+    public void removeLoanFor(User borrower) {
+        loanMap.remove(borrower);
+    }
+
+    public void showDebt() {
+        for (Map.Entry<User, Double> entry : debtMap.entrySet()) {
+            System.out.println(name + " owes " + entry.getKey().name + " : " + Math.abs(entry.getValue()));
+        }
+    }
+
+    public void showLoan() {
+        for (Map.Entry<User, Double> entry : loanMap.entrySet()) {
+            System.out.println(entry.getKey().name + " owes " + name + " : " + Math.abs(entry.getValue()));
+        }
+    }
+}

Splitwise/modeselector/SplitModeSelector.java

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+package Designs.Splitwise.modeselector;
+
+import Designs.Splitwise.splitmodes.SplitMode;
+
+import java.util.Map;
+
+public class SplitModeSelector {
+    private Map<SplitTypes, SplitMode> map;
+
+    public SplitModeSelector(Map<SplitTypes, SplitMode> map) {
+        this.map = map;
+    }
+
+    public SplitMode select(SplitTypes type) {
+        return map.get(type);
+    }
+}

Splitwise/modeselector/SplitTypes.java

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+package Designs.Splitwise.modeselector;
+
+public enum SplitTypes {
+    EQUAL, EXACT, PERCENT
+}

Splitwise/parser/Parser.java

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+package Designs.Splitwise.parser;
+
+import Designs.Splitwise.machine.Machine;
+
+public class Parser {
+    private final Machine machine;
+
+    public Parser(Machine machine) {
+        this.machine = machine;
+    }
+
+    public void parse(String cmd) {
+        String[] tokens = cmd.split(" ");
+        if (tokens[0].equals("SHOW")) {
+            if (tokens.length == 1) {
+                machine.showAll();
+            } else if (tokens.length == 2) {
+                machine.showBalanceFor(tokens[1]);
+            }
+        } else if (tokens[0].equals("EXPENSE")) {
+            machine.addExpense(tokens);
+        }
+    }
+}

Splitwise/splitmodes/EqualSplitMode.java

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+package Designs.Splitwise.splitmodes;
+
+import Designs.Splitwise.model.User;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+public class EqualSplitMode extends SplitMode {
+
+    @Override
+    public void addExpense(Map<String, User> usersMap, String[] tokens) {
+        initialise(tokens, usersMap);
+
+        double equalShare = expenseToAdd / users.size();
+
+        for (User borrower : users) {
+            if (borrower == lender) continue;
+            // lender side
+            updateLenderPortfolio(lender, equalShare, borrower);
+
+            // borrower side
+            updateBorrowerPortfolio(lender, equalShare, borrower);
+        }
+    }
+
+}

Splitwise/splitmodes/ExactSplitMode.java

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+package Designs.Splitwise.splitmodes;
+
+import Designs.Splitwise.model.User;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+public class ExactSplitMode extends SplitMode {
+
+    @Override
+    public void addExpense(Map<String, User> usersMap, String[] tokens) {
+        initialise(tokens, usersMap);
+
+        List<Double> expenseDistribution = populateExpenseDistribution(tokens);
+        boolean isValid = validate(expenseToAdd, expenseDistribution);
+        if (!isValid) {
+            System.out.println("Invalid input");
+            return;
+        }
+
+        int j = 0;
+        for (User borrower : users) {
+            double exactShare = expenseDistribution.get(j++);
+            if (borrower == lender) continue;
+            // lender side
+            updateLenderPortfolio(lender, exactShare, borrower);
+
+            // borrower side
+            updateBorrowerPortfolio(lender, exactShare, borrower);
+        }
+    }
+
+    private boolean validate(double expenseToAdd, List<Double> expenseDistribution) {
+        double sum = 0;
+        for (Double d : expenseDistribution) {
+            sum += d;
+        }
+        return expenseToAdd == sum;
+    }
+}

Splitwise/splitmodes/PercentSplitMode.java

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+package Designs.Splitwise.splitmodes;
+
+import Designs.Splitwise.model.User;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+
+public class PercentSplitMode extends SplitMode {
+
+    @Override
+    public void addExpense(Map<String, User> usersMap, String[] tokens) {
+        initialise(tokens, usersMap);
+
+        List<Double> expenseDistribution = populateExpenseDistribution(tokens);
+        boolean isValid = validate(expenseDistribution);
+        if (!isValid) {
+            System.out.println("Invalid input");
+            return;
+        }
+
+        int j = 0;
+        for (User borrower : users) {
+            double percent = expenseDistribution.get(j++);
+            double exactShare = percent / 100 * expenseToAdd;
+            if (borrower == lender) continue;
+            // lender side
+            updateLenderPortfolio(lender, exactShare, borrower);
+
+            // borrower side
+            updateBorrowerPortfolio(lender, exactShare, borrower);
+        }
+    }
+
+    private boolean validate(List<Double> expenseDistribution) {
+        double sum = 0;
+        for (Double d : expenseDistribution) {
+            sum += d;
+        }
+        return sum == 100.0;
+    }
+
+}