Search for a Value in Linked List in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the linked list contains the target value.

DSA Rust

fn contains(head: &Option<Box<Node>>, target: i32) -> bool {
    let mut current = head;
    while let Some(node) = current {
        if node.value == [1] {
            return true;
        }
        current = &node.next;
    }
    false
}

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

Avalue

Bnode

Chead

Dtarget

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with the wrong variable like 'node' or 'head' instead of 'target'.

Using 'value' without specifying the node.

We compare the current node's value with the target value to find if it exists in the list.

2fill in blank

medium

Complete the code to move to the next node in the linked list during search.

DSA Rust

fn contains(head: &Option<Box<Node>>, target: i32) -> bool {
    let mut current = head;
    while let Some(node) = current {
        if node.value == target {
            return true;
        }
        current = &node.[1];
    }
    false
}

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

Anext

Bchild

Cprev

Dlink

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'prev' which is for doubly linked lists, not singly linked lists.

Using incorrect field names like 'child' or 'link'.

To traverse the linked list, we move from the current node to its 'next' node.

3fill in blank

hard

Fix the error in the code to correctly return false when the value is not found.

DSA Rust

fn contains(head: &Option<Box<Node>>, target: i32) -> bool {
    let mut current = head;
    while let Some(node) = current {
        if node.value == target {
            return true;
        }
        current = &node.next;
    }
    [1]
}

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

Areturn

Btrue

Cfalse

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Returning true by mistake at the end.

Returning None which is not a boolean.

If the loop finishes without finding the target, the function should return false.

4fill in blank

hard

Fill both blanks to create a function that searches for a value and returns its position (index) or -1 if not found.

DSA Rust

fn find_index(head: &Option<Box<Node>>, target: i32) -> i32 {
    let mut current = head;
    let mut index = 0;
    while let Some(node) = current {
        if node.value == [1] {
            return index;
        }
        current = &node.[2];
        index += 1;
    }
    -1
}

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

Atarget

Bvalue

Cprev

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong field names like 'prev' for singly linked list.

Comparing with 'value' instead of 'target'.

We compare with 'target' and move to the 'next' node while counting the index.

5fill in blank

hard

Fill all three blanks to create a function that returns true if the linked list contains any value greater than the target.

DSA Rust

fn contains_greater(head: &Option<Box<Node>>, target: i32) -> bool {
    let mut current = head;
    while let Some(node) = current {
        if node.[1] [2] [3] {
            return true;
        }
        current = &node.next;
    }
    false
}

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

Avalue

B>

Ctarget

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for comparison.

Comparing with wrong variables or fields.

We check if node.value is greater than the target value.

Practice

1. What is the main purpose of searching for a value in a linked list?

easy

A. To find if a specific value exists in the list

B. To add a new node at the end of the list

C. To delete the first node of the list

D. To reverse the order of nodes in the list

Solution

1. Step 1: Understand the search operation

   Searching in a linked list means checking each node to see if it contains the value we want.

2. Step 2: Identify the goal of searching

   The goal is to find whether the value exists anywhere in the list, not to modify the list.

3. Final Answer:

   To find if a specific value exists in the list -> Option A

4. Quick Check:

   Search means find value [OK]

Hint: Search means check each node for the value [OK]

Common Mistakes:

• Confusing search with insertion or deletion
• Thinking search changes the list
• Assuming search reverses the list

2. Which Rust code snippet correctly starts a search for a value in a linked list node called head?

easy

A. let current = head.as_mut();

B. let current = head.unwrap();

C. let mut current = head.unwrap();

D. let mut current = head.as_ref();

Solution

1. Step 1: Understand linked list node type in Rust

   Linked list nodes are often wrapped in Option and Box, so head is Option.

2. Step 2: Choose safe way to start traversal

   Using head.as_ref() gives an Option reference to the node without moving ownership, allowing safe traversal.

3. Final Answer:

   let mut current = head.as_ref(); -> Option D

4. Quick Check:

   Use as_ref() to borrow node safely [OK]

Hint: Use as_ref() to get a reference without moving ownership [OK]

Common Mistakes:

• Using unwrap() which can panic if list is empty
• Using as_mut() when only reading values
• Not using mut when needing to traverse

3. What will be the output of this Rust code searching for value 5 in the linked list 1 -> 3 -> 5 -> 7?

struct Node {
    value: i32,
    next: Option,
}

fn search(head: &Option, target: i32) -> bool {
    let mut current = head.as_ref();
    while let Some(node) = current {
        if node.value == target {
            return true;
        }
        current = node.next.as_ref();
    }
    false
}

fn main() {
    let list = Some(Box::new(Node { value: 1, next: Some(Box::new(Node { value: 3, next: Some(Box::new(Node { value: 5, next: Some(Box::new(Node { value: 7, next: None })) })) })) }));
    println!("{}", search(&list, 5));
}

medium

A. false

B. true

C. Compilation error

D. Runtime panic

Solution

1. Step 1: Trace the search function

   The function starts at head (value 1), checks 1 != 5, moves to 3, checks 3 != 5, moves to 5, finds 5 == 5, returns true.

2. Step 2: Confirm output of main

   Main prints the boolean returned by search, which is true.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Value found in list = true [OK]

Hint: Follow nodes until value matches or list ends [OK]

Common Mistakes:

• Assuming search returns false without checking all nodes
• Confusing Option types causing compile errors
• Forgetting to use as_ref() when traversing

4. Identify the bug in this Rust function that searches for a value in a linked list:

fn search(head: &Option, target: i32) -> bool {
    let mut current = head.unwrap();
    while current.is_some() {
        if current.value == target {
            return true;
        }
        current = current.next.unwrap();
    }
    false
}

medium

A. Incorrect comparison operator used

B. Missing mut keyword for current variable

C. Using unwrap() on Option without checking can cause panic

D. Function does not return a boolean

Solution

1. Step 1: Analyze unwrap() usage

   Calling unwrap() on Option without checking if it is Some can cause the program to panic if the list is empty or next is None.

2. Step 2: Explain safe alternative

   Using as_ref() and pattern matching with while let Some(node) = current avoids panics by safely handling None cases.

3. Final Answer:

   Using unwrap() on Option without checking can cause panic -> Option C

4. Quick Check:

   Unsafe unwrap causes panic [OK]

Hint: Never unwrap Option without checking Some first [OK]

Common Mistakes:

• Ignoring possibility of None causing panic
• Not using while let for safe traversal
• Assuming unwrap always safe

5. Given a linked list where each node contains an integer, how would you modify the search function to return the position (0-based index) of the first occurrence of a target value, or -1 if not found? Choose the correct Rust code snippet.

struct Node {
    value: i32,
    next: Option,
}

fn search_position(head: &Option, target: i32) -> i32 {
    // Fill in the code
}

hard

A. let mut current = head.as_ref(); let mut index = 0; while let Some(node) = current { if node.value == target { return index; } current = node.next.as_ref(); index += 1; } -1

B. let mut current = head.unwrap(); let mut index = 0; while current.is_some() { if current.value == target { return index; } current = current.next.unwrap(); index += 1; } -1

C. let mut current = head.as_ref(); let mut index = 1; while let Some(node) = current { if node.value == target { return index; } current = node.next.as_ref(); index += 1; } 0

D. let mut current = head.as_ref(); let mut index = 0; while let Some(node) = current { if node.value != target { return index; } current = node.next.as_ref(); index += 1; } -1

Solution

1. Step 1: Initialize traversal and index

   Start with current as a reference to head and index at 0 to count positions from start.

2. Step 2: Traverse nodes checking values

   Use while let Some(node) to safely traverse. If node.value equals target, return current index. Otherwise, move to next node and increment index.

3. Step 3: Return -1 if not found

   If loop ends without finding target, return -1 to indicate absence.

4. Final Answer:

   let mut current = head.as_ref(); let mut index = 0; while let Some(node) = current { if node.value == target { return index; } current = node.next.as_ref(); index += 1; } -1 -> Option A

5. Quick Check:

   Return index if found, else -1 [OK]

Hint: Return index on match, else -1 after full traversal [OK]

Common Mistakes:

• Starting index at 1 instead of 0
• Returning index when value does not match
• Using unwrap() causing panic on empty list