Kth Largest Element Using Max Heap in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a max heap from the vector.

DSA Rust

let mut heap = std::collections::BinaryHeap::[1](nums);

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Awith_capacity

Bnew

Cfrom

Ddefault

Attempts:

3 left

💡 Hint

Common Mistakes

Using new() creates an empty heap, not from a vector.

with_capacity() only reserves space, does not build from vector.

We use BinaryHeap::from to create a max heap from an existing vector.

2fill in blank

medium

Complete the code to pop the largest element from the max heap.

DSA Rust

let largest = heap.[1]().unwrap();

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Apeek

Bpop

Cremove

Dextract

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek() only returns a reference, does not remove the element.

remove() and extract() are not methods of BinaryHeap.

pop() removes and returns the largest element from the max heap.

3fill in blank

hard

Fix the error in the loop that pops k-1 largest elements.

DSA Rust

for _ in 0..[1] {
    heap.pop();
}

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Ak+1

Bk

Ck * 2

Dk-1

Attempts:

3 left

💡 Hint

Common Mistakes

Popping k times removes the kth largest too early.

Using k+1 or k*2 causes out of range or logic errors.

We pop k-1 times to remove the top k-1 largest elements before getting the kth.

4fill in blank

hard

Fill both blanks to return the kth largest element safely.

DSA Rust

match heap.[1]() {
    Some(val) => val,
    None => [2],
}

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Apop

Bpanic!("Heap is empty")

C0

Dunwrap()

Attempts:

3 left

💡 Hint

Common Mistakes

Using peek() instead of pop() does not remove the element.

Returning 0 silently hides errors.

pop() removes the top element; if heap is empty, panic with a message.

5fill in blank

hard

Fill all three blanks to implement kth_largest function using max heap.

DSA Rust

fn kth_largest(nums: Vec<i32>, k: usize) -> i32 {
    let mut heap = std::collections::BinaryHeap::[1](nums);
    for _ in 0..[2] {
        heap.[3]();
    }
    heap.pop().expect("Heap is empty")
}

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

Afrom

Bk-1

Cpop

Dnew

Attempts:

3 left

💡 Hint

Common Mistakes

Using new() creates empty heap, not from nums.

Looping k times removes kth largest too early.

Using peek() instead of pop() does not remove elements.

Create heap from vector, pop k-1 times, then pop kth largest element.

Practice

1. What is the main idea behind finding the kth largest element using a max heap?

easy

A. Sort the array and pick the element at index k

B. Build a max heap from the array and extract the maximum element k times

C. Build a min heap and extract the minimum element k times

D. Use a hash map to count frequencies and find the kth largest

Solution

1. Step 1: Understand max heap property

   A max heap always keeps the largest element at the root, so extracting the root gives the current largest element.

2. Step 2: Extract max k times

   By removing the root k times, the last extracted element is the kth largest.

3. Final Answer:

   Build a max heap and extract max k times -> Option B

4. Quick Check:

   Max heap extraction = kth largest [OK]

Hint: Extract max from max heap k times to get kth largest [OK]

Common Mistakes:

• Using min heap instead of max heap
• Sorting instead of using heap
• Extracting fewer or more than k times

2. Which of the following Rust code snippets correctly creates a max heap from a vector nums?

easy

A. let mut heap = std::collections::BinaryHeap::from(nums);

B. let mut heap = std::collections::BinaryHeap::new(nums);

C. let mut heap = std::collections::BinaryHeap::build(nums);

D. let mut heap = std::collections::BinaryHeap::max(nums);

Solution

1. Step 1: Check Rust BinaryHeap constructors

   The correct way to create a max heap from a vector is using BinaryHeap::from().

2. Step 2: Verify other options

   new() creates an empty heap, build() and max() do not exist.

3. Final Answer:

   let mut heap = std::collections::BinaryHeap::from(nums); -> Option A

4. Quick Check:

   Use from() to build heap from vector [OK]

Hint: Use BinaryHeap::from(vector) to create max heap from vector [OK]

Common Mistakes:

• Using new() with vector argument
• Calling non-existent methods like build()
• Confusing min heap creation with max heap

3. What is the output of the following Rust code snippet?

use std::collections::BinaryHeap;

fn main() {
    let nums = vec![3, 1, 5, 12, 2, 11];
    let mut heap = BinaryHeap::from(nums);
    let mut kth_largest = 0;
    for _ in 0..3 {
        kth_largest = heap.pop().unwrap();
    }
    println!("{}", kth_largest);
}

medium

A. 3

B. 11

C. 5

D. 12

Solution

1. Step 1: Build max heap from vector

   The max heap will have elements ordered with largest at root: 12, 11, 5, 3, 2, 1.

2. Step 2: Pop max element 3 times

   First pop: 12, second pop: 11, third pop: 5. So kth_largest is 5.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   3rd largest element = 5 [OK]

Hint: Pop max heap k times; last popped is kth largest [OK]

Common Mistakes:

• Confusing 3rd largest with 2nd or 1st largest
• Not popping enough times
• Assuming heap is sorted array

4. Identify the error in the following Rust code that tries to find the 2nd largest element using a max heap:

use std::collections::BinaryHeap;

fn main() {
    let nums = vec![4, 7, 1, 3];
    let mut heap = BinaryHeap::new();
    for &num in &nums {
        heap.push(num);
    }
    let mut kth_largest = 0;
    for _ in 0..2 {
        heap.pop();
        kth_largest = heap.peek().unwrap().clone();
    }
    println!("{}", kth_largest);
}

medium

A. Using peek() after pop() causes incorrect kth largest value

B. BinaryHeap::new() cannot be used to create a heap

C. The loop should run 3 times instead of 2

D. Using clone() on peek() is unnecessary and causes error

Solution

1. Step 1: Understand peek() vs pop()

   peek() returns reference to max element but does not remove it; pop() removes it.

2. Step 2: Analyze loop behavior

   Loop uses pop() to remove the current max without assigning it, then peek() to assign the next max. For k=2, it discards 7 and 4, assigning 4 then 3, so kth_largest = 3 (incorrect; should be 4).

3. Final Answer:

   Using peek() after pop() causes incorrect kth largest value -> Option A

4. Quick Check:

   pop before peek skips current max [OK]

Hint: Use pop() to get and remove max; peek() only views [OK]

Common Mistakes:

• Using peek() instead of pop() to get kth largest
• Confusing peek() and pop() behavior
• Incorrect loop count for kth element

5. Given a large vector nums with 1 million elements, which approach is most efficient to find the 10th largest element using Rust's max heap?

hard

A. Build a max heap from all elements and pop 10 times

B. Sort the entire vector and pick the 10th element from the end

C. Use a hash map to count frequencies and find the 10th largest

D. Build a min heap of size 10 and iterate through all elements

Solution

1. Step 1: Analyze max heap approach

   Building a max heap of 1 million elements and popping 10 times is O(n + k log n), which is costly.

2. Step 2: Consider min heap of size 10

   Maintaining a min heap of size 10 while iterating all elements keeps track of top 10 largest efficiently in O(n log k) time.

3. Step 3: Compare with sorting and hash map

   Sorting is O(n log n), slower than min heap approach; hash map frequency counting is not suitable for large distinct values.

4. Final Answer:

   Build a min heap of size 10 and iterate through all elements -> Option D

5. Quick Check:

   Min heap size k is efficient for large data [OK]

Hint: Use min heap of size k for large data to find kth largest efficiently [OK]

Common Mistakes:

• Building max heap of all elements for large data
• Sorting entire large vector unnecessarily
• Using frequency map for large distinct values