Programming Fundamentals and Code Quality Questions

from typing import List

def binary_search(arr: List[int], target: int) -> int:
    """
    Iterative binary search on sorted ascending array.
    Returns index of target or -1 if not found.
    """
    left, right = 0, len(arr) - 1
    while left <= right:                      # inclusive bounds
        mid = left + (right - left) // 2
        if arr[mid] == target:
            return mid
        elif arr[mid] < target:
            left = mid + 1                    # move past mid
        else:
            right = mid - 1                   # move before mid
    return -1

from typing import Protocol, Any
class Preprocessor(Protocol):
    def transform(self, record: dict) -> dict: ...
class Trainer:
    def __init__(self, model, optimizer, loss_fn, train_loader, val_loader, device='cpu'): ...
    def train(self, epochs:int): ...

from collections import Counter
import heapq
from typing import List

def top_k_frequent(nums: List[int], k: int) -> List[int]:
    # Count frequencies: O(n)
    freq = Counter(nums)
    # Min-heap of (frequency, num). Keep size k -> O(n log k)
    heap = []
    for num, f in freq.items():
        if len(heap) < k:
            heapq.heappush(heap, (f, num))
        else:
            # If current frequency larger than smallest in heap, replace
            if f > heap[0][0]:
                heapq.heapreplace(heap, (f, num))
    # Extract results (order not guaranteed by frequency descending)
    return [num for (_, num) in heapq.nlargest(k, heap)]