Bottom View of Binary Tree in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the struct for a binary tree node.

DSA Rust

struct Node {
    data: i32,
    left: Option<Box<Node>>,
    right: Option<Box<Node>>,
}

impl Node {
    fn new(data: i32) -> Self {
        Node {
            data,
            left: [1],
            right: None,
        }
    }
}

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

ASome(Node::new(data))

BSome(Box::new(Node::new(data)))

CNone

DBox::new(Node::new(data))

Attempts:

3 left

💡 Hint

Common Mistakes

Using Some without boxing the node.

Initializing left child with a new node instead of None.

The left child is initially empty, so it should be None.

2fill in blank

medium

Complete the code to insert a node into the binary tree at the correct horizontal distance.

DSA Rust

use std::collections::HashMap;

fn bottom_view(root: &Option<Box<Node>>, hd: i32, map: &mut HashMap<i32, i32>) {
    if let Some(node) = root {
        map.insert(hd, node.data);
        bottom_view(&node.left, hd - 1, map);
        [1](&node.right, hd + 1, map);
    }
}

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

Abottom_view

Binsert

Ctraverse

Dvisit

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong function name causing compilation error.

Not calling recursively on the right child.

The function calls itself recursively on the right child to update the map.

3fill in blank

hard

Fix the error in the code to print the bottom view of the binary tree in order of horizontal distance.

DSA Rust

fn print_bottom_view(map: &HashMap<i32, i32>) {
    let mut keys: Vec<i32> = map.keys().cloned().collect();
    keys.sort();
    for key in keys {
        print!("{} ", [1]);
    }
    println!();
}

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

Amap[key]

Bmap.get(&key).unwrap()

Ckey

Dmap[&key]

Attempts:

3 left

💡 Hint

Common Mistakes

Using map[key] which is invalid syntax in Rust.

Using key instead of value in print.

HashMap values are accessed with get(&key) and unwrap to get the value.

4fill in blank

hard

Fill both blanks to create a HashMap and call the bottom_view function starting from root with horizontal distance 0.

DSA Rust

use std::collections::HashMap;

fn main() {
    let mut map: HashMap<i32, i32> = [1];
    let root = Some(Box::new(Node::new(10)));
    bottom_view(&root, [2], &mut map);
    print_bottom_view(&map);
}

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

AHashMap::new()

B0

C1

DHashMap::default()

Attempts:

3 left

💡 Hint

Common Mistakes

Using HashMap::default() which is less common.

Starting horizontal distance at 1 instead of 0.

We create an empty HashMap with HashMap::new() and start horizontal distance at 0.

5fill in blank

hard

Fill all three blanks to update the bottom view map with the current node's data and recursively traverse left and right children with updated horizontal distances.

DSA Rust

fn bottom_view(root: &Option<Box<Node>>, hd: i32, map: &mut HashMap<i32, i32>) {
    if let Some(node) = root {
        map.[1](hd, node.data);
        bottom_view(&node.[2], hd [3] 1, map);
        bottom_view(&node.right, hd + 1, map);
    }
}

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

Ainsert

Bleft

C-

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove instead of insert.

Using '+' instead of '-' for left child horizontal distance.

We insert the node data at horizontal distance, recurse left with hd - 1, and right with hd + 1.

Practice

1. What does the bottom view of a binary tree represent?

easy

A. Nodes visible when the tree is viewed from the left side

B. Nodes visible when the tree is viewed from the top

C. Nodes visible when the tree is viewed from the bottom

D. Nodes visible when the tree is viewed from the right side

Solution

1. Step 1: Understand the bottom view concept

   The bottom view shows nodes visible when looking at the tree from below, meaning the lowest nodes at each horizontal distance.

2. Step 2: Compare with other views

   Top view shows nodes from above, left and right views show nodes from sides, so bottom view is unique for bottom perspective.

3. Final Answer:

   Nodes visible when the tree is viewed from the bottom -> Option C

4. Quick Check:

   Bottom view = nodes visible from below [OK]

Hint: Bottom view shows lowest nodes at each horizontal distance [OK]

Common Mistakes:

• Confusing bottom view with top view
• Thinking bottom view is left or right side view
• Assuming all nodes are visible in bottom view

2. Which Rust data structure is best suited to store nodes by their horizontal distance when computing bottom view?

easy

A. Vec<Node>

B. HashMap

C. LinkedList<Node>

D. BinaryHeap<Node>

Solution

1. Step 1: Identify the need for horizontal distance mapping

   We need to map horizontal distances (integers) to nodes, so a key-value structure is required.

2. Step 2: Choose appropriate Rust data structure

   HashMap allows storing nodes with horizontal distance keys efficiently.

3. Final Answer:

   HashMap<i32, Node> -> Option B

4. Quick Check:

   Use HashMap for horizontal distance mapping [OK]

Hint: Use HashMap to map horizontal distance to nodes [OK]

Common Mistakes:

• Using Vec which doesn't map keys to values
• Using LinkedList which is sequential, not key-based
• Using BinaryHeap which is for priority, not mapping

3. Given the following Rust code snippet for bottom view, what is the printed output?

struct Node {
    val: i32,
    left: Option,
    right: Option,
}

// Tree:
//       1
//      / \
//     2   3
//      \   \
//       4   5

// Bottom view expected: 2 -> 4 -> 3 -> 5

fn main() {
    // Assume bottom_view function returns Vec<i32> of bottom view nodes
    let bottom = vec![2, 4, 3, 5];
    for val in bottom {
        print!("{} -> ", val);
    }
    print!("null\n");
}

medium

A. 2 -> 3 -> 4 -> 5 -> null

B. 1 -> 2 -> 3 -> 4 -> 5 -> null

C. 4 -> 2 -> 5 -> 3 -> null

D. 2 -> 4 -> 3 -> 5 -> null

Solution

1. Step 1: Understand the tree structure and bottom view

   The tree has nodes 2,4,3,5 visible from bottom at horizontal distances -1,0,1,2 respectively.

2. Step 2: Trace the printed output from the vector

   The vector contains [2,4,3,5], printed with arrows and ending with null.

3. Final Answer:

   2 -> 4 -> 3 -> 5 -> null -> Option D

4. Quick Check:

   Bottom view print matches vector [OK]

Hint: Match printed output with bottom view vector [OK]

Common Mistakes:

• Confusing node order in bottom view
• Printing all nodes instead of bottom view nodes
• Missing the final 'null' in output

4. Identify the bug in this Rust snippet for bottom view calculation:

fn bottom_view(root: Option) -> Vec<i32> {
    let mut map = std::collections::HashMap::new();
    let mut queue = std::collections::VecDeque::new();
    queue.push_back((root.unwrap(), 0));

    while let Some((node, hd)) = queue.pop_front() {
        map.insert(hd, node.val);
        if let Some(left) = node.left {
            queue.push_back((left, hd - 1));
        }
        if let Some(right) = node.right {
            queue.push_back((right, hd + 1));
        }
    }

    let mut keys: Vec<_> = map.keys().cloned().collect();
    keys.sort();
    keys.iter().map(|k| map[k]).collect()
}

medium

A. Using unwrap() on root without checking if it's None

B. Not updating map with bottom-most node at each horizontal distance

C. Incorrect horizontal distance calculation for left child

D. Not sorting keys before collecting bottom view nodes

Solution

1. Step 1: Check root unwrap usage

   Calling unwrap() on root without checking if root is None can cause panic if tree is empty.

2. Step 2: Verify other logic correctness

   Horizontal distances and map updates are correct; keys are sorted before collecting nodes.

3. Final Answer:

   Using unwrap() on root without checking if it's None -> Option A

4. Quick Check:

   unwrap() on None causes panic [OK]

Hint: Check unwrap() usage on Option before unwrapping [OK]

Common Mistakes:

• Ignoring possibility of empty tree causing panic
• Assuming map updates only once per horizontal distance
• Forgetting to sort keys before output

5. You have a binary tree where multiple nodes share the same horizontal distance and depth. How should you modify the bottom view algorithm in Rust to ensure the node with the greatest depth is shown in the bottom view?

hard

A. Store (node value, depth) in the map and update only if new depth >= stored depth

B. Store only node values and overwrite map entry whenever a node is visited

C. Use a stack instead of queue to traverse nodes

D. Sort nodes by value before inserting into the map

Solution

1. Step 1: Understand the need to track depth

   Bottom view requires the lowest node at each horizontal distance, so depth must be tracked.

2. Step 2: Modify map to store node value and depth

   Store tuple (value, depth) and update map only if new node's depth is greater or equal to existing depth.

3. Step 3: Ignore other options

   Overwriting blindly loses depth info; stack changes traversal order; sorting by value doesn't solve depth issue.

4. Final Answer:

   Store (node value, depth) in the map and update only if new depth >= stored depth -> Option A

5. Quick Check:

   Track depth to keep bottom-most node [OK]

Hint: Track depth and update map only if deeper node found [OK]

Common Mistakes:

• Ignoring node depth leading to wrong bottom view
• Overwriting map entries without depth check
• Changing traversal method without addressing depth