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Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).
For example,
S = "ADOBECODEBANC"
T = "ABC"
Minimum window is "BANC".
Note:
If there is no such window in S that covers all characters in T, return the empty string "".
If there are multiple such windows, you are guaranteed that there will always be only one unique minimum window in S.
牛逼的讨论：
https://leetcode.com/discuss/72701/here-10-line-template-that-can-solve-most-substring-problems
另一个讲解：
https://leetcode.com/discuss/18584/sharing-my-straightforward-o-n-solution-with-explanation
[?]**Minimum Window Substring & String类问题模板
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原文地址：http://www.cnblogs.com/hygeia/p/5133265.html
