76. Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".

The testcases will be generated such that the answer is unique.

Note: Hard

     Once missingCount is never negative.

def minWindow(self, s: str, t: str) -> str:

    need, missingCount = collections.Counter(t), len(t)

    i = I = J = 0

    for j, c in enumerate(s, 1):

        missingCount -= need[c] > 0            

        need[c] -= 1

        if missingCount == 0:

            while i < j and need[s[i]] < 0:

                need[s[i]] += 1

                i += 1

            if not J or j - i <= J - I:

                I, J = i, j

    return s[I:J]