Find Anagrams in a Character Stream

Over a stream of characters, report in real time every occurrence of an anagram of a fixed target word using a fixed-size sliding window and a frequency array. Requirements Over a stream of characters, report in real time every occurrence of an anagram of a fixed target word. The window size equals the target length; report each position whose preceding len(target) characters are a permutation of the target. Notes Maintain a fixed-size sliding window with a frequency array (or counter) of the last len(target) chars; compare against the target frequency in O(1) per step using a "matches" counter rather than re-comparing the whole map. Streaming twist: you cannot freely index backward — keep the rolling window state incrementally, adding the incoming char and evicting the one leaving the window. Mind the boundary before the window is full (fewer than len(target) chars seen) and the eviction step on each advance. Equivalent to LC 438 (Find All Anagrams in a String) adapted to an online stream. Preparation Solve LC 438 with the matched-count optimization, then refactor it into a push(char) streaming interface that emits matches as windows complete. Drill the window-full boundary and the evict-then-add ordering.