start = 0, end = 0, count = 0 iterate till first k size window reached: increment end and keep adding to set 1st window size reached - check for distinct when window size==k, check all the k chars ...

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1. partition the array in blocks of size w=4. The last block may have less then w. 2. Traverse the list from start to end and calculate max_so_far. Reset max after each block boundary (of w elements).