原始網址:
http://www.careercup.com/question?id=248673
題目:
Given a document and a query of K words,
how do you find the smallest window that covers all the words at least once
in that document?
(given you know the inverted lists of all K words, that is, for each word,
you have a list of all its occurrrences).
Could someone propose an algorithm in O(n)?
假設 occurrrences lists 是 sorted, 用 TreeMap 應可在 O(N*logK) 解決,
一開始將每個 occurrrences list 最小的丟入 TreeMap 就可得到第一個 window,
(key = index in the document, value = the occurrrences list it belonged & its
index in that occurrrences list),
之後將 TreeMap 最小的移除並加入同一個 occurrrences list 的下一個即可移動
window,
直到任一個 occurrrences list 耗完.
但要在 O(N) 的時間內解決就想不出來了...
不知道板上有沒有人有什麼 idea?