43 lines
1.4 KiB
Python
43 lines
1.4 KiB
Python
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# Time: O(N^2)
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# Space: O(N)
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from collections import Counter
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class Solution:
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def characterReplacement(self, s: str, k: int) -> int:
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'''
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Sliding window approach
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'''
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def window_size(l, r):
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return r - l + 1
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# Need to keep track of frequency of each character in the
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# window
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count = Counter()
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l = r = 0
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result = 0
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while r < len(s):
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# Increment the frequency of the `r`th char
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count.update(s[r])
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# We can perform upto K replacements. So we prefer least num
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# of replacements (<= K). In the current window, we can perform
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# least replacements for the most common character in the range.
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#
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# e.g. AAABB K=2, in range 0 to 4, most common char is A, count=3
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# so it just needs 5 - 3 = 2 replacements which is <= K which is ok.
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#
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# But, if K = 1, then we need 5 - 2 = 2 replacements for the same range
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# but 2 > K so this window is not valid. We need to move left pointer in
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# this case and reduce its count.
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if window_size(l, r) - count.most_common(1)[0][1] > k:
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count.subtract(s[l])
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l += 1
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result = max(result, window_size(l, r))
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r += 1
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return result
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