Solve set equality and ad log top‑K

### Problem Set (Coding) #### 1) Check whether two sets are equal You are given two integer arrays `A` and `B` that represent **sets**, except they may contain duplicates and are not sorted. Return `true` if they represent the same mathematical set (same unique elements), otherwise return `false`. **Example** - `A = [1,2,2,3]`, `B = [3,1,2]` → `true` - `A = [1,2]`, `B = [1,2,4]` → `false` **Constraints** - `0 <= len(A), len(B) <= 2e5` - Values fit in 32-bit signed integer. --- #### 2) Top-K ads from impression logs + sliding window ingestion You are given an impression log as a list of events: - `events[i] = (timestamp_ms, ad_id)` - `events` is sorted by `timestamp_ms` ascending. **Part 1 (batch):** Given `events`, a window size `W_ms`, and an end time `T_end`, return the **top K ad IDs by number of impressions** whose timestamps fall in `[T_end - W_ms, T_end]`. Break ties by smaller `ad_id` (or specify a deterministic rule). **Part 2 (streaming):** Implement a data structure with two operations: - `ingestImpression(timestamp_ms, ad_id)` - `getTopK(T_end, W_ms, K)` such that it efficiently supports a sliding window query over recent impressions. Assume `ingestImpression` timestamps are non-decreasing. --- #### 3) Can a target string be formed from a source string? Given two strings `source` and `target`, determine if you can form `target` using characters from `source`. - Each character in `source` can be used **at most once**. - Return `true` if possible, else `false`. **Example** - `source = "aab"`, `target = "aba"` → `true` - `source = "ab"`, `target = "abb"` → `false` **Constraints** - Strings consist of ASCII letters (you may assume lowercase `a-z` if you want to simplify). - Length up to `2e5`.