Find Top K Elements Practice Problem

This data science coding problem helps you practice Sorting & Searching, find top k elements, and implementation skills. Read the problem statement, write your solution, and strengthen your understanding of Sorting & Searching.

Problem ID: 102
Problem key: 102-find-top-k-elements
URL: https://datacrack.app/solve/102-find-top-k-elements
Difficulty: easy
Topic: Sorting & Searching
Module: Python Fundamentals

Problem Statement

# 🧩 Find Top K Elements

---

### 🎯 Goal
Finding the top-K elements is a daily data science operation: top-K features by importance, top-K predictions by confidence, top-K customers by revenue. This problem teaches partial sorting using Python's `sorted()`.

---

### 🔍 Find Top K Elements
From a list of numbers, return the `k` largest values in **descending order**:
```
nums = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3], k = 3
→ [9, 6, 5]
```

---

### 💻 Task
Implement `top_k(nums, k)` using `sorted()` and slicing.

---

### 📥 Input
- `nums`: list of numbers
- `k`: int — how many top elements to return (k ≤ len(nums))

### 📤 Output
- A list of the `k` largest values, in **descending order**

---

### 🧩 Starter Code
```python
def top_k(nums, k):
    """
    Return the k largest elements in descending order.

    Args:
        nums (list): Input numbers
        k (int): Number of top elements to return

    Returns:
        list: k largest values in descending order
    """
    # 🧠 TODO: Sort nums in descending order
    # 🧠 TODO: Return the first k elements
    pass
```

---

### 💡 Example
```python
top_k([3, 1, 4, 1, 5, 9, 2, 6, 5, 3], 3)
# Expected: [9, 6, 5]
```

---

### 🔑 Key Concepts
- `sorted(nums, reverse=True)` sorts descending
- `[:k]` slices the first k elements
- For very large lists, `heapq.nlargest(k, nums)` is more efficient (O(n log k) vs O(n log n))

Starter Code

def top_k(nums, k):
    """
    Return the k largest elements in descending order.

    Args:
        nums (list): Input numbers
        k (int): Number of top elements to return

    Returns:
        list: k largest values in descending order
    """
    # 🧠 TODO: Sort nums in descending order
    # 🧠 TODO: Return the first k elements
    pass

Find Top K Elements Practice Problem

Problem Statement

Starter Code

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