Exercise 2: K Smallest Elements 🔢

Your Task

Write a function k_smallest(nums, k) that returns the k smallest elements from a list, in sorted order (smallest first).

Use heapq!

Examples

print(k_smallest([5, 3, 8, 1, 4, 2, 7], 3))
# Output: [1, 2, 3]

print(k_smallest([10, 20, 30, 40], 2))
# Output: [10, 20]

print(k_smallest([7, 7, 7, 1], 1))
# Output: [1]

Hints

💡 Hint 1

Check out heapq.nsmallest(k, nums) — it does most of the work!

💡 Hint 2 — Manual approach

You can also do it manually:

Turn the list into a heap with heapq.heapify()
Pop k times with heapq.heappop()
Collect the results

✅ Solution (one-liner)

import heapq

def k_smallest(nums, k):
    return heapq.nsmallest(k, nums)

✅ Solution (manual)

import heapq

def k_smallest(nums, k):
    heap = nums[:]          # Copy so we don't modify original
    heapq.heapify(heap)     # Turn into a min-heap: O(n)
    result = []
    for _ in range(k):
        result.append(heapq.heappop(heap))  # Pop smallest each time
    return result

Why this works: After heapifying, each heappop gives you the next smallest element. Pop k times and you're done!

Bonus Challenge 🌟

Now write k_largest(nums, k) that returns the k largest elements in descending order.

print(k_largest([5, 3, 8, 1, 4, 2, 7], 3))
# Output: [8, 7, 5]

Hint: Try heapq.nlargest(), or use the negate trick — push -val to simulate a max-heap!

K Smallest Elements

Exercise 2: K Smallest Elements 🔢

Your Task

Examples

Hints

Bonus Challenge 🌟

Try it yourself

Code: K Smallest Elements