```python
"""Count the hits a key stream scores on a direct-mapped cache."""
from typing import List

def slot_hits(keys: List[int], slots: int) -> int:
    if not isinstance(keys, list):
        raise ValueError("keys must be a list of integers")
    if not isinstance(slots, int) or slots <= 0:
        raise ValueError("slots must be a positive integer")

    held = [None] * slots
    hits = 0

    for key in keys:
        slot = key % slots
        if held[slot] == key:
            hits += 1
        else:
            held[slot] = key

    return hits
```