Implement an LFU / TTL Cache

Question

## Problem

Implement a cache with TTL expiry and an eviction policy (LFU or LRU) in O(1) operations.

## Example
```
get/put with per-key TTL; evict on capacity
```

## Constraints
- High request rate

## Approach
Hash map + frequency buckets (LFU) or doubly linked list (LRU); lazy TTL on access.