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a problem
By zarif_2002, history, 7 years ago, In English

how can i find out a substring of minimum length having at least k times same character(for example k times a)of a string(please in C)

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7 years ago, hide # |
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Prefix sum the number of occurrences of character c. Then do the binary search for every s[i] and find prefix sum with biggest index j such that d[i]-d[j]>=k (if d[] is prefix sum). Answer is minimum of such i-j+1.

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    7 years ago, hide # ^ |
     
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    what is prefix sum please?

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      Prefix sum is array that for each prefix_sum[i] counts (in this case) number of character c from 0 (if string is 0-indexed) to i. How we do that, well prefix_sum[i]=prefix_sum[i-1]. And if s[i] is certain character that we want, increment prefix_sum[i] by 1.

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