Checking for Keys and Values

Part of the Logic & Flow section of Coddy's Dart journey — lesson 27 of 65.

Before accessing data in a Map, it's essential to verify that the key or value you're looking for actually exists. Dart provides two methods for this: containsKey() and containsValue().

The containsKey() method checks if a specific key exists in the map, returning true if found and false otherwise. This is particularly useful before trying to access a value, helping you avoid potential errors.

Map<String, String> userPermissions = {
  'user123': 'admin',
  'user456': 'editor',
  'user789': 'viewer'
};

bool hasUser = userPermissions.containsKey('user123');
print(hasUser);  // true

bool hasUnknownUser = userPermissions.containsKey('user999');
print(hasUnknownUser);  // false

Similarly, containsValue() checks if a specific value exists anywhere in the map. This method searches through all the values and returns true if it finds a match.

bool hasAdmin = userPermissions.containsValue('admin');
print(hasAdmin);  // true

These methods are crucial for writing safe code that handles missing data gracefully, preventing runtime errors when working with dynamic map contents.

Challenge

Easy

Create a program that manages a user authentication system by verifying user credentials and checking permission levels. Your program should:

Read a string input representing the system name
Read multiple pairs of inputs representing usernames and their permission levels (the input will end when you receive "users_done")
Read a string input representing the username to check
Read a string input representing the permission level to verify
Create a Map to store usernames as keys and their permission levels as values
Use containsKey() to check if the username exists in the system
Use containsValue() to check if the specified permission level exists anywhere in the system
Print the authentication analysis in the exact format shown below

For example, if the system name is "Corporate Network", the users include "alice" with "admin", "bob" with "editor", "charlie" with "viewer", "diana" with "admin", the username to check is "alice", and the permission level to verify is "admin", your program should output:

System: Corporate Network
User Database: {alice: admin, bob: editor, charlie: viewer, diana: admin}
Authentication Check:
Username 'alice' exists: true
Permission 'admin' exists in system: true
User 'alice' has permission 'admin': true
Access Status: GRANTED - User authenticated with valid permissions
Security Level: High (admin access detected)

If the system name is "School Portal", the users include "teacher1" with "instructor", "student1" with "student", "admin1" with "administrator", the username to check is "guest", and the permission level to verify is "student", your program should output:

System: School Portal
User Database: {teacher1: instructor, student1: student, admin1: administrator}
Authentication Check:
Username 'guest' exists: false
Permission 'student' exists in system: true
User 'guest' has permission 'student': false
Access Status: DENIED - Username not found in system
Security Level: Low (user not registered)

If the system name is "Library System", the users include "librarian" with "staff", "member1" with "member", "member2" with "member", the username to check is "librarian", and the permission level to verify is "premium", your program should output:

System: Library System
User Database: {librarian: staff, member1: member, member2: member}
Authentication Check:
Username 'librarian' exists: true
Permission 'premium' exists in system: false
User 'librarian' has permission 'premium': false
Access Status: DENIED - Permission level not available
Security Level: Medium (valid user, invalid permission)

Your program must use containsKey() to verify if the username exists and containsValue() to check if the permission level exists anywhere in the system. To check if the specific user has the specific permission, compare the user's actual permission level with the requested one. Determine the security level based on the results: "High" if access is granted with admin-type permissions (admin, administrator, staff), "Medium" if the user exists but has wrong permissions, and "Low" if the user doesn't exist. The input format will be: system name, then alternating usernames and permission levels, ending with "users_done", followed by the username to check and the permission level to verify.

Cheat sheet

Use containsKey() to check if a specific key exists in a Map:

Map<String, String> userPermissions = {
  'user123': 'admin',
  'user456': 'editor',
  'user789': 'viewer'
};

bool hasUser = userPermissions.containsKey('user123');
print(hasUser);  // true

Use containsValue() to check if a specific value exists anywhere in a Map:

bool hasAdmin = userPermissions.containsValue('admin');
print(hasAdmin);  // true

Both methods return true if found and false otherwise, helping prevent runtime errors when working with dynamic map contents.

Try it yourself

import 'dart:io';

void main() {
  // Read system name
  String? systemName = stdin.readLineSync();
  
  // Create a Map to store usernames and their permission levels
  Map<String, String> userDatabase = {};
  
  // Read user data until "users_done"
  while (true) {
    String? input = stdin.readLineSync();
    if (input == "users_done") {
      break;
    }
    String username = input!;
    String? permission = stdin.readLineSync();
    userDatabase[username] = permission!;
  }
  
  // Read username to check and permission level to verify
  String? usernameToCheck = stdin.readLineSync();
  String? permissionToVerify = stdin.readLineSync();
  
  // TODO: Write your code below
  // Use containsKey() to check if username exists
  // Use containsValue() to check if permission level exists in system
  // Check if the specific user has the specific permission
  // Determine access status and security level:
  //   - "High (admin access detected)" if access granted AND permission is admin, administrator, or staff
  //   - "Medium (standard access)" if access granted but permission is not admin-type
  //   - "Medium (valid user, invalid permission)" if user exists but has wrong permission
  //   - "Low (user not registered)" if user does not exist
  
  // Print the authentication analysis
  print("System: $systemName");
  print("User Database: $userDatabase");
  print("Authentication Check:");
  // Add your output statements here
}