Lists, Maps, and Sets in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a list of strings named fruits.

Flutter

List<String> fruits = [1];

Drag options to blanks, or click blank then click option'

A["apple", "banana", "cherry"]

B("apple", "banana", "cherry")

C{"apple", "banana", "cherry"}

D<"apple", "banana", "cherry">

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses () instead of square brackets []

Using curly braces {} which create sets or maps

Using angle brackets <> which are for generics, not collections

In Dart, lists are created using square brackets [].

2fill in blank

medium

Complete the code to access the value for key 'name' in the map.

Flutter

Map<String, String> person = {"name": "Alice", "city": "Paris"};
String name = person[1];

Drag options to blanks, or click blank then click option'

A[0]

B["name"]

C.name

D("name")

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation which does not work for map keys

Using parentheses which is invalid syntax

Using an index number which is for lists, not maps

To get a value from a map by key, use square brackets with the key as a string.

3fill in blank

hard

Fix the error in the code to add an item to the set.

Flutter

Set<int> numbers = {1, 2, 3};
numbers[1](4);

Drag options to blanks, or click blank then click option'

Apush

Bappend

Cadd

Dinsert

Attempts:

3 left

💡 Hint

Common Mistakes

Using append or push which are list methods

Using insert which is not a method for sets

Trying to add items with assignment instead of a method

Sets use the add() method to add new items.

4fill in blank

hard

Fill both blanks to create a map from a list of keys and a list of values.

Flutter

List<String> keys = ["a", "b", "c"];
List<int> values = [1, 2, 3];
Map<String, int> map = Map.fromIterables([1], [2]);

Drag options to blanks, or click blank then click option'

Akeys

Bvalues

Citems

Delements

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping keys and values

Using undefined variables like items or elements

Passing only one argument instead of two

Map.fromIterables takes two iterables: one for keys and one for values.

5fill in blank

hard

Fill all three blanks to create a set from a list and add a new item.

Flutter

List<int> nums = [1, 2, 3];
Set<int> numSet = [1](nums);
numSet.[2](4);
bool hasFour = numSet.[3](4);

Drag options to blanks, or click blank then click option'

ASet.from

Badd

Ccontains

DList.of

Attempts:

3 left

💡 Hint

Common Mistakes

Using List.of instead of Set.from

Using wrong method names like insert or push

Checking membership with wrong methods

Use Set.from to create a set from a list, add() to add an item, and contains to check membership.

Practice

1. Which of the following correctly describes a Set in Flutter?

easy

A. A fixed-size list that cannot be changed.

B. A collection of key-value pairs for fast lookup.

C. An ordered list that allows duplicate items.

D. A collection of unique items without any specific order.

Solution

1. Step 1: Understand Set characteristics

   A Set stores unique items and does not maintain order.

2. Step 2: Compare with other collections

   Maps store key-value pairs, Lists allow duplicates and are ordered.

3. Final Answer:

   A collection of unique items without any specific order. -> Option D

4. Quick Check:

   Set = unique unordered collection [OK]

Hint: Remember: Sets have unique items, no order [OK]

Common Mistakes:

• Confusing Sets with Lists (which allow duplicates)
• Thinking Sets maintain insertion order
• Mixing up Maps and Sets

2. Which of the following is the correct syntax to create a Map in Flutter?

easy

A. var myMap = {'key1': 'value1', 'key2': 'value2'};

B. var myMap = Set('key1', 'value1');

C. var myMap = ['key1', 'value1', 'key2', 'value2'];

D. var myMap = {1, 2, 3};

Solution

1. Step 1: Identify Map syntax

   Maps use curly braces with key-value pairs separated by colons.

2. Step 2: Check each option

   var myMap = {'key1': 'value1', 'key2': 'value2'}; correctly uses {'key': 'value'} pairs. Others are list, set, or invalid syntax.

3. Final Answer:

   var myMap = {'key1': 'value1', 'key2': 'value2'}; -> Option A

4. Quick Check:

   Map syntax = {'key': 'value'} [OK]

Hint: Maps use curly braces with colon-separated pairs [OK]

Common Mistakes:

• Using commas instead of colons for key-value pairs
• Confusing list syntax with Map syntax
• Trying to create Map with Set syntax

3. What will be the output of this Flutter code?

var list = [1, 2, 3, 2];
var set = list.toSet();
print(set);

medium

A. {1, 2, 3}

B. [1, 2, 3, 2]

C. {1, 2, 3, 2}

D. [1, 2, 3]

Solution

1. Step 1: Convert list to set

   Calling toSet() removes duplicates and creates a Set.

2. Step 2: Understand Set output

   Set prints with curly braces and unique values only: {1, 2, 3}.

3. Final Answer:

   {1, 2, 3} -> Option A

4. Quick Check:

   List to Set removes duplicates [OK]

Hint: toSet() removes duplicates and changes brackets [OK]

Common Mistakes:

• Expecting list brackets [] instead of set braces {}
• Thinking duplicates remain after toSet()
• Confusing output format of Set vs List

4. Identify the error in this Flutter code snippet:

var map = {'a': 1, 'b': 2};
map.add('c', 3);

medium

A. Keys in Map must be integers, not strings.

B. The method add() does not exist for Map.

C. Map cannot have more than two key-value pairs.

D. The syntax for Map declaration is incorrect.

Solution

1. Step 1: Check Map methods

   Maps do not have an add() method; use map[key] = value to add entries.

2. Step 2: Validate other options

   Keys can be strings, Maps can have many pairs, and declaration syntax is correct.

3. Final Answer:

   The method add() does not exist for Map. -> Option B

4. Quick Check:

   Use map[key] = value to add entries [OK]

Hint: Use map[key] = value to add, not add() method [OK]

Common Mistakes:

• Trying to use add() on Map instead of assignment
• Thinking Map keys must be integers
• Assuming Map size is limited

5. Given this Flutter code, what will be the final content of result?

var list = [1, 2, 2, 3];
var map = {for (var i in list) i: i * 2};
var result = map.values.toSet().toList();
print(result);

hard

A. [1, 4, 6]

B. [1, 2, 3]

C. [2, 4, 6]

D. [2, 2, 4, 6]

Solution

1. Step 1: Create Map from list

   Map comprehension uses list items as keys and doubles as values. Duplicate keys overwrite, so map = {1:2, 2:4, 3:6}.

2. Step 2: Extract values and remove duplicates

   map.values = [2, 4, 6]. Converting to Set removes duplicates (none here), then toList() keeps order.

3. Final Answer:

   [2, 4, 6] -> Option C

4. Quick Check:

   Map keys unique, values doubled, duplicates removed [OK]

Hint: Map keys unique; duplicates overwrite values [OK]

Common Mistakes:

• Expecting duplicate keys to keep all entries
• Confusing keys and values in map comprehension
• Not converting Set back to List