Implement an LFU cache

## Problem: LFU Cache Design and implement a **Least Frequently Used (LFU) cache** with a fixed capacity. The cache supports the following operations: - `get(key) -> value` - Return the value of `key` if it exists in the cache. - Otherwise return `-1`. - If the key exists, its **usage frequency** increases by 1. - `put(key, value) -> void` - Insert or update the value of `key`. - If the cache reaches capacity, it must evict one key before inserting. ### Eviction Policy 1. Evict the key with the **lowest frequency** (LFU). 2. If multiple keys have the same (lowest) frequency, evict the **least recently used** (LRU) among them. ### Requirements / Constraints - Capacity is a non-negative integer. - Aim for **O(1)** average time per operation. - If `capacity == 0`, `put` does nothing and `get` always returns `-1`. ### Example If capacity = 2: - `put(1, 1)` - `put(2, 2)` - `get(1)` returns `1` (freq(1)=2) - `put(3, 3)` evicts key `2` (freq(2)=1 is lowest) - `get(2)` returns `-1` - `get(3)` returns `3`