LFU cache

Implement an LFU (Least-Frequently-Used) cache with the given positive capacity. get(key) returns the value or -1 if absent. put(key, value) inserts or updates; when at capacity, evict the least-frequently-used key, breaking ties by least-recently-used. Both get and put count as a use that increments the key's frequency. Given a list of operations (['put', k, v] or ['get', k]), return the list of results produced by get operations, in order (put produces no output). There are 1 to 10^4 ops; capacity is between 1 and 10^4.