Keyword Alert - Monitor Text Streams and Trigger Alerts on Keyword Matches

Question

## Round 1 - Coding

## Problem

Design a keyword alerting system. Users register alert rules specifying a keyword and a callback. As text messages stream in, fire all matching callbacks.

```python
class KeywordAlert:
    def register(
        self,
        keyword: str,
        callback: callable,
        case_sensitive: bool = False
    ) -> int:
        # Returns rule_id
        ...

def unregister(self, rule_id: int) -> bool: ...

def process(self, message: str) -> int:
        # Fire callbacks for all matching rules
        # Returns count of rules triggered
        ...
```

```
Example:
alert = KeywordAlert()
alert.register("error", lambda m: print(f"ALERT: {m}"))
alert.register("ERROR", lambda m: print(f"STRICT: {m}"), case_sensitive=True)

alert.process("System error detected")  # fires rule 1 only -> 1
alert.process("ERROR in module")        # fires rule 1 and rule 2 -> 2
alert.process("All clear")              # fires nothing -> 0
```

## Follow-ups

1. How would you handle multi-keyword rules (e.g. alert if message contains BOTH "error" AND "critical")?
2. What data structure enables O(1) average keyword lookup vs. O(k) scan of all rules?
3. How would you scale this to 100K concurrent alert rules?
4. How would you add rate limiting so a single rule fires at most once per minute?

Keyword Alert - Monitor Text Streams and Trigger Alerts on Keyword Matches

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